Systems and methods for multi-stage air dehumidification and cooling

ABSTRACT

The present disclosure relates to systems and methods for dehumidifying air by establishing a humidity gradient across a water selective permeable membrane in a dehumidification unit. Water vapor from relatively humid atmospheric air entering the dehumidification unit is extracted by the dehumidification unit without substantial condensation into a low pressure water vapor chamber operating at a partial pressure of water vapor lower than the partial pressure of water vapor in the relatively humid atmospheric air. For example, water vapor is extracted through a water permeable membrane of the dehumidification unit into the low pressure water vapor chamber. As such, the air exiting the dehumidification unit is less humid than the air entering the dehumidification unit. The low pressure water vapor extracted from the air is subsequently condensed and removed from the system at ambient conditions.

This application is a Non-Provisional patent application of U.S.Provisional Patent Application No. 61/413,327, entitled “Systems andMethods for Air Dehumidification and Cooling”, filed Nov. 12, 2010,which is incorporated by reference in its entirety herein.

BACKGROUND

Heating, ventilating, and air conditioning (HVAC) systems often havedehumidification systems integrated into the cooling apparatus fordehumidifying the air being conditioned by such systems. When cooling isrequired in warm to hot environments, the air being cooled anddehumidified will usually have a humidity ratio above approximately0.009 (pounds of H₂O per pounds of dry air). In these environments, theHVAC systems traditionally use refrigerant compressors for sensiblecooling of the air and removal of latent energy (i.e., humidity). Theair is typically cooled to about 55° F., which condenses H₂O out of theair until the air is about 100% saturated (i.e., relative humidity atabout 100%). The 55° F. temperature lowers the humidity ratio to about0.009 pounds of H₂O per pound of dry air, which is the water vaporsaturation point at 55° F., resulting in a relative humidity of almost100%. When this air warms to about 75° F., the humidity ratio remainsapproximately the same, and the relative humidity drops to approximately50%. This traditional method of dehumidification requires the air to becooled to about 55° F., and can usually achieve a coefficient ofperformance (COP) of approximately 3-5.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of embodiments of thepresent disclosure will become better understood when the followingdetailed description is read with reference to the accompanying drawingsin which like characters represent like parts throughout the drawings,wherein:

FIG. 1 is a schematic diagram of an HVAC system having adehumidification unit in accordance with an embodiment of the presentdisclosure;

FIG. 2A is a perspective view of the dehumidification unit of FIG. 1having multiple parallel air channels and water vapor channels inaccordance with an embodiment of the present disclosure;

FIG. 2B is a perspective view of the dehumidification unit of FIG. 1having a single air channel located inside a single water vapor channelin accordance with an embodiment of the present disclosure;

FIG. 3 is a plan view of an air channel and adjacent water vaporchannels of the dehumidification unit of FIGS. 1, 2A, and 2B inaccordance with an embodiment of the present disclosure;

FIG. 4 is a perspective view of a separation module formed using amembrane that may be used as a water vapor channel of thedehumidification unit of FIGS. 1-3 in accordance with an embodiment ofthe present disclosure;

FIG. 5 is a psychrometric chart of the temperature and the humidityratio of the moist air flowing through the dehumidification unit ofFIGS. 1-3 in accordance with an embodiment of the present disclosure;

FIG. 6 is a schematic diagram of the HVAC system and thedehumidification unit of FIG. 1 having a vacuum pump for removingnoncondensable components from the water vapor in the water vaporextraction chamber of the dehumidification unit in accordance with anembodiment of the present disclosure;

FIG. 7 is a schematic diagram of the HVAC system and thedehumidification unit of FIG. 6 having a control system for controllingvarious operating conditions of the HVAC system and the dehumidificationunit in accordance with an embodiment of the present disclosure;

FIG. 8 is a schematic diagram of an HVAC system having a plurality ofdehumidification units arranged in series in accordance with anembodiment of the present disclosure;

FIG. 9 is a schematic diagram of an HVAC system having a plurality ofdehumidification units arranged in parallel in accordance with anembodiment of the present disclosure;

FIG. 10 is a schematic diagram of an HVAC system having a firstplurality of dehumidification units arranged in series, and a secondplurality of dehumidification units also arranged in series, with thefirst and second plurality of dehumidification units arranged inparallel in accordance with an embodiment of the present disclosure;

FIG. 11 is a schematic diagram of an HVAC system having an evaporativecooling unit disposed upstream of the dehumidification unit inaccordance with an embodiment of the present disclosure;

FIG. 12A is a psychrometric chart of the temperature and the humidityratio of the air flowing through a direct evaporative cooling unit andthe dehumidification unit of FIG. 11 in accordance with an embodiment ofthe present disclosure;

FIG. 12B is a psychrometric chart of the temperature and the humidityratio of the air flowing through an indirect evaporative cooling unitand the dehumidification unit of FIG. 11 in accordance with anembodiment of the present disclosure;

FIG. 13 is a schematic diagram of an HVAC system having the evaporativecooling unit disposed downstream of the dehumidification unit inaccordance with an embodiment of the present disclosure;

FIG. 14A is a psychrometric chart of the temperature and the humidityratio of the air flowing through the dehumidification unit and a directevaporative cooling unit of FIG. 13 in accordance with an embodiment ofthe present disclosure;

FIG. 14B is a psychrometric chart of the temperature and the humidityratio of the air flowing through the dehumidification unit and anindirect evaporative cooling unit of FIG. 13 in accordance with anembodiment of the present disclosure;

FIG. 15A is a psychrometric chart of the temperature and the humidityratio of the air flowing through a plurality of dehumidification unitsand a plurality of direct evaporative cooling units in accordance withan embodiment of the present disclosure;

FIG. 15B is a psychrometric chart of the temperature and the humidityratio of the air flowing through a plurality of dehumidification unitsand a plurality of indirect evaporative cooling units in accordance withan embodiment of the present disclosure;

FIG. 16 is a schematic diagram of an HVAC system having a mechanicalcooling unit disposed downstream of the dehumidification unit inaccordance with an embodiment of the present disclosure;

FIG. 17 is a schematic diagram of an HVAC system having the mechanicalcooling unit of FIG. 16 disposed upstream of the dehumidification unitin accordance with an embodiment of the present disclosure;

FIG. 18 is a schematic diagram of an HVAC system usingmini-dehumidification units in accordance with an embodiment of thepresent disclosure;

FIG. 19 is a schematic diagram of an HVAC system using multiple coolingand dehumidification stages disposed in series, in accordance with anembodiment of the present disclosure;

FIG. 20 is a schematic diagram of the HVAC system of FIG. 19, includinga control system;

FIG. 21 is a schematic diagram of an HVAC system using multiple coolingand dehumidification stages disposed in parallel and in series, inaccordance with an embodiment of the present disclosure;

FIG. 22 is a schematic diagram of an HVAC system using multipledehumidification units disposed in series and fluidly coupled to acooling system disposed downstream of the multiple dehumidificationunits, in accordance with an embodiment of the present disclosure;

FIG. 23 is a schematic diagram of an HVAC system using multipledehumidification units disposed in series and fluidly coupled to acooling system disposed upstream of the multiple dehumidification units,in accordance with an embodiment of the present disclosure;

FIG. 24 is a schematic diagram of an HVAC system using multipledehumidification units disposed in parallel and fluidly coupled to acooling system disposed downstream of the multiple dehumidificationunits, in accordance with an embodiment of the present disclosure;

FIG. 25 is a schematic diagram of an HVAC system using multipledehumidification units disposed in parallel and fluidly coupled to acooling system disposed upstream of the multiple dehumidification units,in accordance with an embodiment of the present disclosure; and

FIG. 26 is a schematic diagram of an HVAC system using multipledehumidification units disposed in parallel and in series and fluidlycoupled to a cooling system disposed downstream of the multipledehumidification units, in accordance with an embodiment of the presentdisclosure.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Specific embodiments of the present disclosure will be described herein.In an effort to provide a concise description of these embodiments, allfeatures of an actual implementation may not be described in thespecification. It should be appreciated that in the development of anysuch actual implementation, as in any engineering or design project,numerous implementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which may vary from one implementation toanother. Moreover, it should be appreciated that such a developmenteffort might be complex and time-consuming, but would nevertheless be aroutine undertaking of design, fabrication, and manufacture for those ofordinary skill having the benefit of this disclosure.

When introducing elements of various embodiments of the presentinvention, the articles “a,” “an,” “the,” and “said” are intended tomean that there are one or more of the elements. The terms “comprising,”“including,” and “having” are intended to be inclusive and mean thatthere may be additional elements other than the listed elements.

The subject matter disclosed herein relates to dehumidification systemsand, more specifically, to systems and methods capable of dehumidifyingair without initial condensation by establishing a humidity gradient ina dehumidification unit. In one embodiment, a water vapor permeablematerial (i.e., a water vapor permeable membrane) is used along at leastone boundary separating an air channel from a secondary channel orchamber to facilitate the removal of water vapor from the air passingthrough the air channel. The secondary channel or chamber separated fromthe air channel by the water vapor permeable material may receive watervapor extracted from the air channel via the water vapor permeablematerial.

In operation, the water vapor permeable material allows the flow of H₂O(which may refer to H₂O as water molecules, gaseous water vapor, liquidwater, adsorbed/desorbed water molecules, absorbed/desorbed watermolecules, or combinations thereof) through the water vapor permeablematerial from the air channel to the secondary channel or chamber, whilesubstantially blocking the flow of other components of the air flowingthrough the air channel from passing through the water vapor permeablematerial. As such, the water vapor permeable material reduces thehumidity of the air flowing through the air channel by removingprimarily only water vapor from the air. Correspondingly, the secondarychannel or chamber is filled with primarily water vapor. It should benoted that the passage of H₂O through the water vapor permeable materialmay be facilitated by a pressure differential. Indeed, a lower partialpressure of water vapor (i.e., a partial pressure less than the partialpressure of water vapor in the air channel) may be created in thesecondary channel or chamber to further facilitate passage of the H₂Othrough the water vapor permeable material. Accordingly, the side of thewater vapor permeable material opposite the air channel may be referredto as the suction side of the water vapor permeable material.

Once the H₂O has been passed through the water vapor permeable material,a vacuum pump is used to increase the partial pressure of the watervapor on the suction side of the water vapor permeable material to aminimal saturation pressure used to enable condensation of the watervapor by a condenser. That is, the vacuum pump compresses the watervapor to a pressure in a range suitable for condensing the water vaporinto liquid water (e.g., a range of approximately 0.25-1.1 pounds persquare inch absolute (psia), with the higher value applying toembodiments using multiple dehumidification units in series), dependingon desired conditions for condensation. The condenser then condenses thewater vapor into a liquid state, and the resulting liquid water is thenpressurized to approximately atmospheric pressure, such that the liquidwater may be rejected at ambient atmospheric conditions. By condensingthe water vapor to a liquid state prior to expelling it, certainefficiencies are provided. For example, pressurizing liquid water toatmospheric pressure uses less energy than pressurizing water vapor toatmospheric pressure. Alternatively, the water vapor may be rejected toambient conditions through a membrane water vapor rejection unit. Itshould also be noted that the dehumidification unit described herein ingeneral uses significantly less energy than conventional systems.

While the embodiments described herein are primarily presented asenabling the removal of water vapor from air, other embodiments mayenable the removal of other H₂O components from air. For example, incertain embodiments, instead of a water vapor permeable material, an H₂Opermeable material may be used. As such, the H₂O permeable material mayallow the flow of one, all, or any combination of H₂O components (i.e.,water molecules, gaseous water vapor, liquid water, adsorbed/desorbedwater molecules, absorbed/desorbed water molecules, and so forth)through the H₂O permeable material from the air channel to the secondarychannel or chamber, while substantially blocking the flow of othercomponents of the air flowing through the air channel from passingthrough the H₂O permeable material. In other words, the disclosedembodiments are not limited to the removal of water vapor from air, butrather to the removal of H₂O (i.e., in any of its states) from air.However, for conciseness, the embodiments described herein are primarilyfocused on the removal of water vapor from air.

In certain embodiments, as described in more detail below with respectto FIGS. 19-26, one or more of the aforementioned dehumidification unitsmay be combined with one or more cooling systems, such as evaporativecooler systems. In one example, multiple stages, each stage includingone evaporative or mechanical cooler and one dehumidification unit, maybe combined in series and/or in parallel. Outside air may enter a firststage of the multiple stages, and be subsequently directed throughmultiple stages, exiting a final stage as cooler, drier air. That is,each subsequent stage may cool and dry the air from the previous stage.In one embodiment, a multi-stage vacuum pump may be used to create a lowpressure side, providing a partial pressure differential suitable forenabling the outside air to move through the multiple stages. In otherembodiments, multiple pumps may be used alternative or additional to themulti-stage pump. The low pressure side may also include a purge unituseful in removing certain components of the air, such as noncondensablecomponents (e.g., oxygen, nitrogen, and other atmospheric gascomponents). A condenser may also be provided, suitable for condensingwater vapor which may then be directed into a liquid receiver. A pumpmay then discharge the liquid from the receiver. Controller systems maybe communicatively coupled to the various components of the multiplestages (e.g., pumps, valves, condensers, evaporative coolers) and usedto more efficiently control the drying and cooling of the air.

By providing for the aforementioned multiple stages, each stageincluding an evaporator or mechanical cooler and a dehumidificationsystem, a drier, cooler air may be produced in a more efficient manner,when compared to using a single stage. Additionally, including themultiple stages may enhance reliability and provide for redundancy. Forexample, bypass valves may be used to bypass certain stages in the eventof an unexpected maintenance event. Indeed, maintenance, including thecomplete removal of one or more stages, may be performed, for example,by using the bypass valves, while the remaining stages may continuedrying and/or cooling operations. Further, each stage may be provided atdifferent producing capacities (e.g., drying, cooling capacity), thusenabling an HVAC system suitable for use in a variety of conditions.

With the foregoing in mind, it may be useful to describe certain systemsand methods, such as an HVAC system 10 depicted in FIG. 1. Morespecifically, FIG. 1 is a schematic diagram of an HVAC system 10 havinga dehumidification unit 12 in accordance with an embodiment of thepresent disclosure. As illustrated, the dehumidification unit 12 mayreceive inlet air 14A having a relatively high humidity and expel outletair 14B having a relatively low humidity. In particular, thedehumidification unit 12 may include one or more air channels 16 throughwhich the air 14 (i.e., the inlet air 14A and the outlet air 14B) flows.In addition, the dehumidification unit 12 may include one or more watervapor channels 18 adjacent to the one or more air channels 16. Asillustrated in FIG. 1, the air 14 does not flow through the water vaporchannels 18. Rather, the embodiments described herein enable the passageof water vapor from the air 14 in the air channels 16 to the water vaporchannels 18, thus dehumidifying the air 14 and accumulating water vaporin the water vapor channels 18. In particular, water vapor from the air14 in the air channels 16 may be allowed to flow through an interface 20(i.e., a barrier or membrane) between adjacent air channels 16 and watervapor channels 18, while the other components (e.g., nitrogen, oxygen,carbon dioxide, and so forth) of the air 14 are blocked from flowingthrough the interface 20. In general, the water vapor channels 18 aresealed to create the low pressure that pulls the water vapor from theair 14 in the air channels 16 through the interfaces 20 as H₂O (i.e., aswater molecules, gaseous water vapor, liquid water, adsorbed/desorbedwater molecules, absorbed/desorbed water molecules, and so forth,through the interfaces 20).

As such, a humidity gradient is established between the air channels 16and adjacent water vapor channels 18. The humidity gradient is generatedby a pressure gradient between the air channels 16 and adjacent watervapor channels 18. In particular, the partial pressure of water vapor inthe water vapor channels 18 is maintained at a level lower than thepartial pressure of water vapor in the air channels 16, such that thewater vapor in the air 14 flowing through the air channels 16 tendstoward the suction side (i.e., the water vapor channels 18 having alower partial pressure of water vapor) of the interfaces 20.

Components of air other than H₂O may be substantially blocked frompassing through the interfaces 20 in accordance with presentembodiments. In other words, in certain embodiments, approximately 95%or more, approximately 96% or more, approximately 97% or more,approximately 98% or more, or approximately 99% or more of components ofthe air 14 other than H₂O (e.g., nitrogen, oxygen, carbon dioxide, andso forth) may be blocked from passing through the interfaces 20. Whencompared to an ideal interface 20 that blocks 100% of components otherthan H₂O, an interface 20 that blocks 99.5% of components other than H₂Owill experience a reduction in efficiency of approximately 2-4%. Assuch, the components other than H₂O may be periodically purged tominimize these adverse effects on efficiency.

FIG. 2A is a perspective view of the dehumidification unit 12 of FIG. 1having multiple parallel air channels 16 and water vapor channels 18 inaccordance with an embodiment of the present disclosure. In theembodiment illustrated in FIG. 2A, the air channels 16 and the watervapor channels 18 are generally rectilinear channels, which provide asubstantial amount of surface area of the interfaces 20 between adjacentair channels 16 and water vapor channels 18. Further, the generallyrectilinear channels 16, 18 enable the water vapor 26A to be removedalong the path of the air channels 16 before the air 14 exits the airchannels 16. In other words, the relatively humid inlet air 14A (e.g.,air with a dew point of 55° F. or higher such that the air isappropriate for air conditioning) passes straight through the airchannels 16 and exits as relatively dry outlet air 14B, because moisturehas been removed as the air 14 traverses along the atmospheric pressureside of the interfaces 20 (i.e., the side of the interfaces 20 in theair channels 16). In an embodiment where a single unit is dehumidifyingto a 60° F. saturation pressure or below, the suction side of theinterfaces 20 (i.e., the side of the interfaces 20 in the water vaporchannels 18) will generally be maintained at a partial pressure of watervapor that is lower than the partial pressure of water vapor on theatmospheric pressure side of the interfaces 20.

As illustrated in FIG. 2A, each of the water vapor channels 18 isconnected with a water vapor channel outlet 22 through which the watervapor in the water vapor channels 18 is removed. As illustrated in FIG.2A, in certain embodiments, the water vapor channel outlets 22 may beconnected via a water vapor outlet manifold 24, wherein the water vapor26A from all of the water vapor channels 18 is combined in a singlewater vapor vacuum volume 28, such as a tube or a chamber. Otherconfigurations of the air channels 16 and the water vapor channels 18may also be implemented. As another example, FIG. 2B is a perspectiveview of the dehumidification unit 12 of FIG. 1 having a single airchannel 16 located inside a single water vapor channel 18 in accordancewith an embodiment of the present disclosure. As illustrated, the airchannel 16 may be a cylindrical air channel located within a largerconcentric cylindrical water vapor channel 18. The embodimentsillustrated in FIGS. 2A and 2B are merely exemplary and are not intendedto be limiting.

FIG. 3 is a plan view of an air channel 16 and adjacent water vaporchannels 18 of the dehumidification unit 12 of FIGS. 1, 2A, and 2B inaccordance with an embodiment of the present disclosure. In FIG. 3, adepiction of the water vapor 26 is exaggerated for illustrationpurposes. In particular, the water vapor 26 from the air 14 is shownflowing through the interfaces 20 between the air channel 16 and theadjacent water vapor channels 18 as H₂O (i.e., as water molecules,gaseous water vapor, liquid water, adsorbed/desorbed water molecules,absorbed/desorbed water molecules, and so forth, through the interfaces20). Conversely, other components 30 (e.g., nitrogen, oxygen, carbondioxide, and so forth) of the air 14 are illustrated as being blockedfrom flowing through the interfaces 20 between the air channel 16 andthe adjacent water vapor channels 18.

In certain embodiments, the interfaces 20 may include membranes that arewater vapor permeable and allow the flow of H₂O through permeablevolumes of the membranes while blocking the flow of the other components30. Again, it should be noted that when the H₂O passes through theinterfaces 20, it may actually pass as one, all, or any combination ofstates of water (e.g., as water vapor, liquid water, adsorbed/desorbedwater molecules, absorbed/desorbed water molecules, and so forth)through the interfaces 20. For example, in one embodiment, theinterfaces 20 may adsorb/desorb water molecules. In another example, theinterfaces 20 may adsorb/desorb water molecules and enable passage ofwater vapor. In other embodiments, the interfaces 20 may facilitate thepassage of water in other combinations of states. The interfaces 20extend along the flow path of the air 14. As such, the water vapor 26 iscontinuously removed from one side of the interface 20 as the relativelyhumid inlet air 14A flows through the air channel 16. Therefore,dehumidification of the air 14 flowing through the air channel 16 isaccomplished by separating the water vapor 26 from the other components30 of the air 14 incrementally as it progresses along the flow path ofthe air channel 16 and continuously contacts the interfaces 20 adjacentto the air channel 16 from the inlet air 14A location to the outlet air14B location.

In certain embodiments, the water vapor channels 18 are evacuated beforeuse of the dehumidification unit 12, such that a lower partial pressureof the water vapor 26 (i.e., a partial pressure less than the partialpressure of water vapor in the air channels 16) is created in the watervapor channels 18. For example, the partial pressure of the water vapor26 in the water vapor channels 18 may be in the range of approximately0.10-0.25 psia during normal operation, which corresponds todehumidifying to a 60° F. saturation pressure or below. In this example,an initial pressure of approximately 0.01 psia may be used to removeother air components (e.g., noncondensables such as oxygen, nitrogen,and carbon dioxide), whereas the partial pressure of water vapor in theair channels 16 may be in the range of approximately 0.2-1.0 psia.However, at certain times, the pressure differential between the partialpressure of the water vapor in the water vapor channels 18 and the airchannels 16 may be as low as (or lower than) approximately 0.01 psia.The lower partial pressure of water vapor in the water vapor channels 18further facilitates the flow of water vapor 26 from the air channels 16to the water vapor channels 18, because the air 14 flowing through theair channels 16 is at local atmospheric pressure (i.e., approximately14.7 psia at sea level). Since the partial pressure of water vapor inthe air 14 in the air channels 16 is greater than the partial pressureof the water vapor 26 in the water vapor channels 18, a pressuregradient is created from the air channels 16 to the water vapor channels18. As described previously, the interfaces 20 between adjacent airchannels 16 and water vapor channels 18 provide a barrier, and allowsubstantially only water vapor 26 to flow from the air 14 in the airchannels 16 into the water vapor channels 18. As such, the air 14flowing through the air channels 16 will generally decrease in humidityfrom the inlet air 14A to the outlet air 14B.

The use of water vapor permeable membranes as the interfaces 20 betweenthe air channels 16 and the water vapor channels 18 has many advantages.In particular, in some embodiments, no additional energy is used togenerate the humidity gradient from the air channels 16 to the watervapor channels 18. In addition, in some embodiments, no regeneration isinvolved and no environmental emissions (e.g., solids, liquids, orgases) are generated. Indeed, in accordance with one embodiment,separation of the water vapor 26 from the other components 30 of the air14 via water permeable membranes (i.e., the interfaces 20) can beaccomplished at energy efficiencies much greater than compressortechnology used to condense water directly from the airstream.

Because water vapor permeable membranes are highly permeable to watervapor, the costs of operating the dehumidification unit 12 may beminimized because the air 14 flowing through the air channels 16 doesnot have to be significantly pressurized to facilitate the passage ofH₂O through the interfaces 20. Water vapor permeable membranes are alsohighly selective to the permeation of the water vapor from the air 14.In other words, water vapor permeable membranes are very efficient atblocking components 30 of the air 14 other than water vapor fromentering the water vapor channels 18. This is advantageous because theH₂O passes through the interfaces 20 due to a pressure gradient (i.e.,due to the lower partial pressures of water vapor in the water vaporchannels 18) and any permeation or leakage of air 14 into the watervapor channels 18 will increase the power consumption of the vacuum pumpused to evacuate the water vapor channels 18. In addition, water vaporpermeable membranes are rugged enough to be resistant to aircontamination, biological degradation, and mechanical erosion of the airchannels 16 and the water vapor channels 18. Water vapor permeablemembranes may also be resistant to bacteria attachment and growth inhot, humid air environments in accordance with one embodiment.

One example of a material used for the water vapor permeable membranes(i.e., the interfaces 20) is zeolite supported on thin, porous metalsheets. In particular, in certain embodiments, an ultrathin (e.g., lessthan approximately 2 μm), zeolite membrane film may be deposited on anapproximately 50 μm thick porous metal sheet. The resulting membranesheets may be packaged into a membrane separation module to be used inthe dehumidification unit 12. FIG. 4 is a perspective view of aseparation module 32 formed using a membrane that may be used as a watervapor channel 18 of the dehumidification unit 12 of FIGS. 1-3 inaccordance with an embodiment of the present disclosure. Two membranesheets 34, 36 may be folded and attached together into a generallyrectangular shape with a channel for the water vapor having a widthw_(msm) of approximately 5 mm. The separation module 32 may bepositioned within the dehumidification unit 12 such that the membranecoating surface is exposed to the air 14. The thinness of the metalsupport sheet reduces the weight and cost of the raw metal material andalso minimizes resistance to the H₂O diffusing through the water vaporpermeable membrane film deposited on the membrane sheets 34, 36. Themetallic nature of the sheets 34, 36 provides mechanical strength andflexibility for packaging such that the separation module 32 canwithstand a pressure gradient of greater than approximately 60 psi(i.e., approximately 4 times atmospheric pressure).

Separation of water vapor from the other components 30 of the air 14 maycreate a water vapor permeation flux of approximately 1.0 kg/m²/h (e.g.,in a range of approximately 0.5-2.0 kg/m²/h), and a water vapor-to-airselectivity range of approximately 5-200+. As such, the efficiency ofthe dehumidification unit 12 is relatively high compared to otherconventional dehumidification techniques with a relatively low cost ofproduction. As an example, approximately 7-10 m² of membrane area of theinterfaces 20 may be used to dehumidify 1 ton of air cooling load underambient conditions. In order to handle such an air cooling load, incertain embodiments, 17-20 separation modules 32 having a height h_(msm)of approximately 450 mm, a length l_(msm) of approximately 450 mm, and awidth w_(msm) of approximately 5 mm may be used. These separationmodules 32 may be assembled side-by-side in the dehumidification unit12, leaving approximately 2 mm gaps between the separation modules 32.These gaps define the air channels 16 through which the air 14 flows.The measurements described in this example are merely exemplary and notintended to be limiting.

FIG. 5 is a psychrometric chart 38 of the temperature and the humidityratio of the moist air 14 flowing through the dehumidification unit 12of FIGS. 1-3 in accordance with an embodiment of the present disclosure.In particular, the x-axis 40 of the psychrometric chart 38 correspondsto the temperature of the air 14 flowing through the air channels 16 ofFIG. 1, the y-axis 42 of the psychrometric chart 38 corresponds to thehumidity ratio of the air 14 flowing through the air channels 16, andthe curve 44 represents the water vapor saturation curve of the air 14flowing through the air channels 16. As illustrated by line 46, becausewater vapor is removed from the air 14 flowing through the air channels16, the humidity ratio of the outlet air 14B (i.e., point 48) from thedehumidification unit 12 of FIGS. 1-3 is lower than the humidity ratioof the inlet air 14A (i.e., point 50) into the dehumidification unit 12of FIGS. 1-3, while the temperature of the outlet air 14B and the inletair 14A are substantially the same.

Returning now to FIG. 1, as described previously, a lower partialpressure of the water vapor 26 (i.e., a partial pressure less than thepartial pressure of water vapor in the air channels 16) is created inthe water vapor channels 18 of the dehumidification unit 12 to furtherfacilitate the passage of H₂O through the interfaces 20 from the airchannels 16 to the water vapor channels 18. In certain embodiments, thewater vapor channels 18 may initially be evacuated using a vacuum pump52. In particular, the vacuum pump 52 may evacuate the water vaporchannels 18 and the water vapor vacuum volume 28, as well as the watervapor outlets 22 and the water vapor manifold 24 of FIG. 2A. However, inother embodiments, a pump separate from the vacuum pump 52 may be usedto evacuate the water vapor channels 18, water vapor vacuum volume 28,water vapor outlets 22, and water vapor manifold 24. As illustrated inFIG. 1, the water vapor 26 removed from the air 14 in thedehumidification unit 12 may be distinguished between the water vapor26A in the water vapor vacuum volume 28 (i.e., the suction side of thevacuum pump 52) and the water vapor 26B expelled from an exhaust side(i.e., an outlet) of the vacuum pump 52 (i.e., the water vapor 26Bdelivered to a condensation unit). In general, the water vapor 26Bexpelled from the vacuum pump 52 will have a slightly higher pressureand a higher temperature than the water vapor 26A in the water vaporvacuum volume 28. The vacuum pump 52 may be a compressor or any othersuitable pressure increasing device capable of maintaining a lowerpressure on the suction side of the vacuum pump 52 than the partialpressure of water vapor in the humid air 14.

For example, the lower partial pressure of water vapor 26A maintained inthe water vapor vacuum volume 28 may be in the range of approximately0.15-0.25 psia, which corresponds to saturation temperatures ofapproximately 45° F. to 60° F., with the water vapor 26A in the range ofapproximately 65-75° F. However, in other embodiments, the water vapor26A in the water vapor vacuum volume 28 may be maintained at a partialpressure of water vapor in the range of approximately 0.01-0.25 psia anda temperature in the range of approximately 55° F. up to the highestambient air temperature. A specific embodiment may be designed to lowerthe partial pressure in the water vapor vacuum volume 28 to the range of0.01 psia to increase the capacity for removing water vapor from the air14 to enable an evaporative cooler to process the entire airconditioning load when atmospheric conditions permit this mode ofoperation.

In certain embodiments, the vacuum pump 52 is a low-pressure pumpconfigured to decrease the pressure of the water vapor 26A in the watervapor vacuum volume 28 to a lower partial pressure than the partialpressure of water vapor on the atmospheric side of the interfaces 20(i.e., the partial pressure of the air 14 in the air channels 16). Onthe exhaust side of the vacuum pump 52, the partial pressure of thewater vapor 26B has been increased just high enough to facilitatecondensation of the water vapor (i.e., in a condensation unit 54).Indeed, the vacuum pump 52 is configured to increase the pressure suchthat the water vapor 26B in the condensation unit 54 is at a pressureproximate to a minimal saturation pressure in the condensation unit 54.Alternatively, the condensation unit 54 and subsequent components may bereplaced by a membrane water vapor rejection unit.

As an example operation of the HVAC system 10, the air 14 may enter thesystem at a partial pressure of water vapor of 0.32 psia, whichcorresponds to a humidity ratio of approximately 0.014 pounds of H₂O perpounds of dry air. The system may be set to remove approximately 0.005pounds of H₂O per pounds of dry air from the air 14. Pressuredifferentials across the interfaces 20 may be used to create a flow ofH₂O through the interfaces 20. For example, the partial pressure ofwater vapor in the water vapor vacuum volume 28 may be set toapproximately 0.1 psia. The pressure of the water vapor 26B is increasedby the vacuum pump 52 in a primarily adiabatic process, and as thepressure of the water vapor 26B increases, the temperature increases aswell (in contrast to the relatively negligible temperature differentialacross the interfaces 20). As such, if for example the pressure of thewater vapor 26B is increased in the vacuum pump 52 by approximately 0.3psi (i.e., to approximately 0.4 psia), the condensation unit 54 is thencapable of condensing the water vapor 26B at a temperature ofapproximately 72-73° F., and the temperature of the water vapor 26Bincreases to a temperature substantially higher than the condensertemperature. The system may continually monitor the pressure andtemperature conditions of both the upstream water vapor 26A and thedownstream water vapor 26B to ensure that the water vapor 26B expelledfrom the vacuum pump 52 has a partial pressure of water vapor just highenough to facilitate condensation in the condensation unit 54. It shouldbe noted that the pressure and temperature values presented in thisscenario are merely exemplary and are not intended to be limiting.

As the pressure difference from the water vapor 26A entering the vacuumpump 52 to the water vapor 26B exiting the vacuum pump 52 increases, theefficiency of the dehumidification unit 12 decreases. For example, inone embodiment, the vacuum pump 52 may be set to adjust the pressure ofthe water vapor 26B in the condensation unit 54 slightly above thesaturation pressure at the lowest ambient temperature of the coolingmedia (i.e., air or water) used by the condensation unit 54 to condensethe water vapor 26B. In another embodiment, the temperature of the watervapor 26B may be used to control the pressure in the condensation unit54. The temperature of the water vapor 26B expelled from the vacuum pump52 may be substantially warmer than the humid air 14A (e.g., thistemperature could reach approximately 200° F. or above depending on avariety of factors). Because the vacuum pump 52 may only increases thepressure of the water vapor 26B to a point where condensation of thewater vapor 26B is facilitated (i.e., approximately the saturationpressure), the power requirements of the vacuum pump 52 are relativelysmall, thereby obtaining a high efficiency from the dehumidificationunit 12.

Once the water vapor 26B has been slightly pressurized (i.e.,compressed) by the vacuum pump 52, the water vapor 26B is directed intothe condensation unit 54, wherein the water vapor 26B is condensed intoa liquid state. In certain embodiments, the condensation unit 54 mayinclude a condensation coil 56, a pipe/tube condenser, a flat platecondenser, or any other suitable system for achieving a temperaturebelow the condensation point of the water vapor 26B. The condensationunit 54 may either be air cooled or water cooled. For example, incertain embodiments, the condensation unit 54 may be cooled by ambientair or water from a cooling tower. As such, the costs of operating thecondensation unit 54 may be relatively low, inasmuch as both ambient airand cooling tower water are in relatively limitless supply.

Once the water vapor 26B has been condensed into a liquid state, incertain embodiments, the liquid water from the condensation unit 54 maybe directed into a reservoir 58 for temporary storage of saturated vaporand liquid water. However, in other embodiments, no reservoir 58 may beused. In either case, the liquid water from the condensation unit 54 maybe directed into a liquid pump 60 (i.e., a water transport device),within which the pressure of the liquid water from the condensation unit54 is increased to approximately atmospheric pressure (i.e.,approximately 14.7 psia) so that the liquid water may be rejected atambient conditions. As such, the liquid pump 60 may be sized just largeenough to increase the pressure of the liquid water from thecondensation unit 54 to approximately atmospheric pressure. Therefore,the costs of operating the liquid pump 60 may be relatively low. Inaddition, the liquid water from the liquid pump 60 may be at a slightlyelevated temperature due to the increase in the pressure of the liquidwater. As such, in certain embodiments, the heated liquid water may betransported for use as domestic hot water for use in the home, furtherincreasing the efficiency of the system by recapturing the heattransferred into the liquid water.

Although the interfaces 20 between the air channels 16 and the watervapor channels 18 as described previously generally allow only H₂O topass from the air channels 16 to the water vapor channels 18, in certainembodiments, very minimal amounts (e.g., less than 1% of the oxygen(O₂), nitrogen (N₂), or other noncondensable components) of the othercomponents 30 of the air 14 may be allowed to pass through theinterfaces 20 from the air channels 16 to the water vapor channels 18.Over time, the amount of the other components 30 may build up in thewater vapor channels 18 (as well as in the water vapor vacuum volume 28,the water vapor outlets 22, and the water vapor manifold 24 of FIG. 2A).In general, these other components 30 are noncondensable at thecondenser temperature ranges used in the condensation unit 54. As such,the components 30 may adversely affect the performance of the vacuumpump 52 and all other equipment downstream of the vacuum pump 52 (inparticular, the condensation unit 54).

Accordingly, in certain embodiments, a second vacuum pump, such as apump 62 shown in FIG. 6, may be used to periodically purge the othercomponents 30 from the water vapor vacuum volume 28. FIG. 6 is aschematic diagram of the HVAC system 10 and the dehumidification unit 12of FIG. 1 having the vacuum pump 62 for removing noncondensablecomponents 30 from the water vapor 26A in the water vapor vacuum volume28 of the dehumidification unit 12 in accordance with an embodiment ofthe present disclosure. The vacuum pump 62 may, in certain embodiments,be the same pump used to evacuate the water vapor vacuum volume 28 (aswell as the water vapor channels 18, the water vapor outlets 22, and thewater vapor manifold 24) to create the lower partial pressure of watervapor described previously that facilitates the passage of the H₂Othrough the interfaces 20 from the air channels 16 to the water vaporchannels 18. However, in other embodiments, the vacuum pump 62 may bedifferent from the pump used to evacuate the water vapor vacuum volume28 to create the lower partial pressure of water vapor.

The dehumidification unit 12 described herein may also be controlledbetween various operating states, and modulated based on operatingconditions of the dehumidification unit 12. For example, FIG. 7 is aschematic diagram of the HVAC system 10 and the dehumidification unit 12of FIG. 6 having a control system 64 for controlling various operatingconditions of the HVAC system 10 and the dehumidification unit 12 inaccordance with an embodiment of the present disclosure. The controlsystem 64 may include one or more processors 66, for example, one ormore “general-purpose” microprocessors, one or more special-purposemicroprocessors and/or ASICS (application-specific integrated circuits),or some combination of such processing components. The processors 66 mayuse input/output (I/O) devices 68 to, for example, receive signals fromand issue control signals to the components of the dehumidification unit12 (i.e., the vacuum pumps 52, 62, the condensation unit 54, thereservoir 58, the liquid pump 60, other equipment such as a fan blowingthe inlet air 14A through the dehumidification unit 12, sensorsconfigured to generate signals related to characteristics of the inletand outlet air 14A, 14B, and so forth). The processors 66 may take thesesignals as inputs and calculate how to control the functionality ofthese components of the dehumidification unit 12 to most efficientlyremove the water vapor 26 from the air 14 flowing through thedehumidification unit 12. The control system 64 may also include anontransitory computer-readable medium (i.e., a memory 70) which, forexample, may store instructions or data to be processed by the one ormore processors 66 of the control system 64.

For example, the control system 64 may be configured to control the rateof removal of the noncondensable components 30 of the water vapor 26Afrom the water vapor vacuum volume 28 of the dehumidification unit 12 byturning the vacuum pump 62 on or off, or by modulating the rate at whichthe vacuum pump 62 removes the noncondensable components 30 of the watervapor 26A. More specifically, in certain embodiments, the control system64 may receive signals from a sensor in the water vapor vacuum volume 28that detects when too many noncondensable components 30 are present inthe water vapor 26A contained in the water vapor vacuum volume 28. Thisprocess of noncondensable component removal may operate in a cyclicalmanner. In “normal” operation of removing the water vapor 26 from theair 14, the vacuum pump 62 may not be in operation. As thenoncondensable components 30 build up in the water vapor vacuum volume28, the internal pressure in the water vapor vacuum volume 28 eventuallyreaches a setpoint. At this point in time, the vacuum pump 62 turns onand removes all components (i.e., both the noncondensable components 30as well as H₂O, including the water vapor) until the internal pressurein the water vapor vacuum volume 28 reaches another setpoint (e.g.,lower than the starting vacuum pressure). Then, the vacuum pump 62 shutsoff and the dehumidification unit 12 returns to the normal operationalmode. Setpoints may either be preset or dynamically determined. Onemethod will be to have the vacuum pump 62 only operating in the purgemode intermittently.

Another example of the type of control that may be accomplished by thecontrol system 64 is modulating the lower partial pressure of the watervapor 26A in the water vapor vacuum volume 28 (as well as the watervapor channels 18, the water vapor outlets 22, and the water vapormanifold 24) to modify the water vapor removal capacity and efficiencyratio of the dehumidification unit 12. For example, the control system64 may receive signals from pressure sensors in the water vapor vacuumvolume 28, the water vapor channels 18, the water vapor outlets 22,and/or the water vapor manifold 24, as well as signals generated bysensors relating to characteristics (e.g., temperature, pressure, flowrate, relative humidity, and so forth) of the inlet and outlet air 14A,14B, among other things. The control system 64 may use this informationto determine how to modulate the lower partial pressure of the watervapor 26A (e.g., with respect to the partial pressure of water vapor inthe air 14 flowing through the air channels 16) to increase or decreasethe rate of removal of water vapor 26 from the air channels 16 to thewater vapor channels 18 through the interfaces 20.

For example, if more water vapor removal is desired, the lower partialpressure of the water vapor 26A in the water vapor vacuum volume 28 maybe reduced and, conversely, if less water vapor removal is desired, thelower partial pressure of the water vapor 26A in the water vapor vacuumvolume 28 may be increased. Furthermore, in certain embodiments, theamount of dehumidification (i.e., water vapor removal) may be cycled toimprove the efficiency of the dehumidification unit 12. Morespecifically, under certain operating conditions, the dehumidificationunit 12 may function more efficiently at higher rates of water vaporremoval. As such, in certain embodiments, the dehumidification unit 12may be cycled to remove a maximum amount of water vapor from the air 14for a period of time (e.g., approximately 1 sec, 10 sec, 100 sec, 10min), then to remove relatively no water vapor from the air 14 for aperiod of time (e.g., approximately 1 sec, 10 sec, 100 sec, 10 min),then to remove a maximum amount of water vapor from the air 14 for aperiod of time (e.g., approximately 1 sec, 10 sec, 100 sec, 10 min), andso forth. In other words, the dehumidification unit 12 may be operatedat full water vapor removal capacity for periods of time alternatingwith other periods of time where no water vapor is removed. In addition,the control system 64 may be configured to control start-up and shutdownsequencing of the dehumidification unit 12.

The dehumidification unit 12 may be designed and operated in manyvarious modes, and at varying operating conditions. In general, thedehumidification unit 12 operates with the water vapor vacuum volume 28(as well as the water vapor channels 18, the water vapor outlets 22, andthe water vapor manifold 24) at a water vapor partial pressure below thewater vapor partial pressure of the air 14 flowing through the airchannels 16. In certain embodiments, the dehumidification unit 12 may beoptimized for dedicated outside air system (DOAS) use, wherein the air14 may have a temperature in the range of approximately 55-100° F., anda relative humidity in the range of approximately 55-100%. In otherembodiments, the dehumidification unit 12 may be optimized forresidential use for recirculated air having a temperature in the rangeof approximately 70-85° F., and a relative humidity in the range ofapproximately 55-65%. Similarly, in certain embodiments, thedehumidification unit 12 may be optimized for dehumidifying outside airin commercial building recirculated air systems, which dehumidifies theinlet air 14A having a temperature in the range of approximately 55-110°F., and a relative humidity in the range of approximately 55-100%. Theoutlet air 14B has less humidity and about the same temperature as theinlet air 14A, unless cooling is performed on the outlet air 14B.

The dehumidification unit 12 described herein uses less operating powerthan conventional dehumidification systems because of the relatively lowpressures that are used to dehumidify the air 14A. This is due at leastin part to the ability of the interfaces 20 (i.e., water vapor permeablemembranes) to remove the water vapor 26 from the air 14 efficientlywithout requiring excessive pressures to force the water vapor 26through the interfaces 20. For example, in one embodiment, the minimalpower used to operate the dehumidification unit 12 includes only the fanpower used to move the air 14 through the dehumidification unit 12, thecompressive power of the vacuum pump 52 to compress the water vapor 26to approximately the saturation pressure (for example, to approximately1.0 psia, or to a saturation pressure that corresponds to a givencondensation temperature, for example, approximately 100° F.), thepumping and/or fan power of the condensation unit 54 (e.g., depending onwhether cooling tower water or ambient air is used as the coolingmedium), the pumping power of the liquid pump 60 to reject the liquidwater from the condensation unit 54 at ambient conditions, and the powerof the vacuum pump 62 to purge noncondensable components 30 that leakinto the water vapor vacuum volume 28 of the dehumidification unit 12.As such, the only relatively major power component used to operate thedehumidification unit 12 is the compressive power of the vacuum pump 52to compress the water vapor 26 to approximately the saturation pressure(for example, only to approximately 1.0 psia, or to a saturationpressure that corresponds to a given condensation temperature, forexample, approximately 100° F.). As mentioned previously, this power isrelatively low and, therefore, operating the dehumidification unit 12 isrelatively inexpensive as opposed to conventional refrigerationcompression dehumidification systems. Moreover, calculations for anembodiment indicate that the dehumidification unit 12 has a coefficientof performance (COP) at least twice as high (or even up to five times ashigh, depending on operating conditions) as these conventionaldehumidification systems. In addition, the dehumidification unit 12enables the dehumidification of air without reducing the temperature ofthe air below the temperature at which the air is needed, as is oftendone in conventional dehumidification systems.

In certain embodiments, multiple instances of the dehumidification unit12 described previously with respect to FIGS. 1 through 7 may be used ina single HVAC system. For example, FIG. 8 is a schematic diagram of anHVAC system 72 having a plurality of dehumidification units 12 (i.e., afirst dehumidification unit 74, a second dehumidification unit 76, and athird dehumidification unit 78) arranged in series in accordance with anembodiment of the present disclosure. Although illustrated as havingthree dehumidification units 74, 76, 78 in series, any number ofdehumidification units 12 may indeed be used in series in the HVACsystem 72. For example, in other embodiments, 2, 4, 5, 6, 7, 8, 9, 10,or even more dehumidification units 12 may be used in series in the HVACsystem 72.

The HVAC system 72 of FIG. 8 generally functions the same as the HVACsystem 10 of FIGS. 1, 6, and 7. More specifically, as illustrated inFIG. 8, the HVAC system 72 receives the inlet air 14A having arelatively high humidity. However, the relatively dry air 14B from thefirst dehumidification unit 74 is not expelled into the atmosphere.Rather, as illustrated in FIG. 8, the air 14B expelled from the firstdehumidification unit 74 is directed into the second dehumidificationunit 76 via a first duct 80. Similarly, air 14C expelled from the seconddehumidification unit 76 is directed into the third dehumidificationunit 78 via a second duct 82. Outlet air 14D from the thirddehumidification unit 78 is then expelled into the conditioned space.Because the dehumidification units 74, 76, 78 of the HVAC system 72 arearranged in series, each successive airstream will be relatively dryerthan the upstream airstreams. For example, outlet air 14D is dryer thanair 14C, which is dryer than air 14B, which is dryer than inlet air 14A.

As illustrated, many of the components of the HVAC system 72 of FIG. 8may be considered identical to the components of the HVAC system 10 ofFIGS. 1, 6, and 7. For example, as described previously, thedehumidification units 74, 76, 78 of the HVAC system 72 of FIG. 8 may beconsidered identical to the dehumidification units 12 of FIGS. 1, 6, and7. In addition, the HVAC system 72 of FIG. 8 also includes thecondensation unit 54 that receives water vapor 26B having a partialpressure just high enough to facilitate condensation, as describedpreviously. In certain embodiments, the HVAC system 72 of FIG. 8 mayalso include the reservoir 58 for temporary storage of saturated vaporand liquid water. However, as described previously, in otherembodiments, no reservoir may be used. In either case, the liquid waterfrom the condensation unit 54 may be directed into the liquid pump 60,within which the pressure of the liquid water from the condensation unit54 is increased to approximately atmospheric pressure (i.e.,approximately 14.7 psia) so that the liquid water may be rejected atambient conditions.

As illustrated in FIG. 8, in certain embodiments, each dehumidificationunit 74, 76, 78 may be associated with a respective vacuum pump 84, 86,88, each of which is similar in functionality to the vacuum pump 52 ofFIGS. 1, 6, and 7. However, because water vapor is removed from eachsuccessive dehumidification unit 74, 76, 78, the partial pressure ofwater vapor in the air 14 may be gradually reduced at each successivedehumidification unit 74, 76, 78. For example, as described previously,the partial pressure of water vapor in the inlet air 14A may be in therange of approximately 0.2-1.0 psia; the partial pressure of water vaporin the air 14B from the first dehumidification unit 74 may be in therange of approximately 0.17-0.75 psia (accomplishing approximately ⅓ ofthe drop); the partial pressure of water vapor in the air 14C from thesecond dehumidification unit 76 may be in the range of approximately0.14-0.54 psia (accomplishing approximately the next ⅓ of the drop); andthe partial pressure of water vapor in the outlet air 14D from the thirddehumidification unit 78 may be in the range of approximately 0.10-0.25psia, which is consistent with a 60° F. saturation temperature or lower.The very low values may be used to increase capacity for occasional use.

As such, in certain embodiments, the partial pressure of water vapor inthe water vapor vacuum volumes 90, 92, 94 (e.g., that are similar infunctionality to the water vapor vacuum volume 28 described previously)associated with each respective vacuum pump 84, 86, 88 may be modulatedto ensure an optimal flow of water vapor 26 from each respectivedehumidification unit 74, 76, 78. For example, the partial pressure ofthe water vapor 26A in the water vapor vacuum volume 28 describedpreviously may be maintained in a range of approximately 0.15-0.25 psia.However, in the HVAC system 72 of FIG. 8, the partial pressure of thewater vapor 26A in the first water vapor vacuum volume 90 may bemaintained in a range of approximately 0.15-0.7 psia, the partialpressure of the water vapor 26A in the second water vapor vacuum volume92 may be maintained in a range of approximately 0.12-0.49 psia, and thepartial pressure of the water vapor 26A in the third water vapor vacuumvolume 94 may be maintained in a range of approximately 0.09-0.24 psia.Regardless, it may be expected that less water vapor 26 is removed ineach successive dehumidification unit 74, 76, 78, and is generally beoptimized to minimize energy used to operate the system.

In certain embodiments, each of the vacuum pumps 84, 86, 88 may compressthe water vapor 26 and direct it into a common manifold 96 having asubstantially constant partial pressure of water vapor (i.e., just highenough to facilitate condensation in the condensation unit 54) such thatthe water vapor 26 flows in a direction opposite to the flow of the air14. In other embodiments, the water vapor 26 extracted from eachsuccessive dehumidification unit 74, 76, 78 may be compressed by itsrespective vacuum pump 84, 86, 88 and then combined with the water vapor26 extracted from the next upstream dehumidification unit 74, 76, 78.For example, in other embodiments, the water vapor 26 from the thirddehumidification unit 78 may be compressed by the third vacuum pump 88and then combined with the water vapor 26 from the seconddehumidification unit 76 in the second water vapor vacuum volume 92.Similarly, the water vapor 26 compressed by the second vacuum pump 86may be combined with the water vapor 26 from the first dehumidificationunit 74 in the first water vapor vacuum volume 90. In this embodiment,the exhaust side of each successive vacuum pump 84, 86, 88 increases thepartial pressure of the water vapor 26 only to the operating pressure ofthe next upstream vacuum pump 84, 86, 88. For example, the third vacuumpump 88 may only increase the pressure of the water vapor 26 toapproximately 0.2 psia if the partial pressure of water vapor in thesecond water vapor vacuum volume 92 is approximately 0.2 psia.Similarly, the second vacuum pump 86 may only increase the pressure ofthe water vapor 26 to approximately 0.35 psia if the partial pressure ofwater vapor in the first water vapor vacuum volume 90 is approximately0.35 psia. In this embodiment, the water vapor 26 compressed by thefirst vacuum pump 84 is directed into the condensation unit 54 at apartial pressure of water vapor just high enough to facilitatecondensation.

It should be noted that the specific embodiment illustrated in FIG. 8having a plurality of dehumidification units 74, 76, 78 arranged inseries may be configured in various ways not illustrated in FIG. 8. Forexample, although illustrated as using a respective vacuum pump 84, 86,88 with each dehumidification unit 74, 76, 78, in certain embodiments, asingle vacuum pump 52 may be used with multiple inlet ports connected tothe first, second, and third water vapor vacuum volumes 90, 92, 94. Inaddition, although illustrated as using a single condensation unit 54,reservoir 58, and liquid pump 60 to condense the water vapor 26B into aliquid state, and store and/or transport the liquid water from the HVACsystem 72, in other embodiments, each set of dehumidification units 74,76, 78 and vacuum pumps 84, 86, 88 may be operated independently and beassociated with their own respective condensation units 54, reservoirs58, and liquid pumps 60.

In addition, the control system 64 of FIG. 7 may also be used in theHVAC system 72 of FIG. 8 to control the operation of the HVAC system 72in a similar manner as described previously with respect to FIG. 7. Forexample, as described previously, the control system 64 may beconfigured to control the rate of removal of the noncondensablecomponents 30 of the water vapor 26 in the water vapor vacuum volumes90, 92, 94 by turning the vacuum pumps 84, 86, 88 (or separate vacuumpumps 62, as described previously with respect to FIGS. 6 and 7) on oroff, or by modulating the rate at which the vacuum pumps 84, 86, 88 (orseparate vacuum pumps 62, as described previously with respect to FIGS.6 and 7) remove the noncondensable components 30. More specifically, incertain embodiments, the control system 64 may receive signals fromsensors in the water vapor vacuum volumes 90, 92, 94 that detect whentoo many noncondensable components 30 are present in the water vapor 26Acontained in the water vapor vacuum volumes 90, 92, 94.

In addition, the control system 64 may modulate the lower partialpressure of the water vapor 26A in the water vapor vacuum volumes 90,92, 94 to modify the water vapor removal capacity and efficiency ratioof the dehumidification units 74, 76, 78. For example, the controlsystem 64 may receive signals from pressure sensors in the water vaporvacuum volumes 90, 92, 94, the water vapor channels 18, as well assignals generated by sensors relating to characteristics (e.g.,temperature, pressure, flow rate, relative humidity, and so forth) ofthe air 14, among other things. The control system 64 may use thisinformation to determine how to modulate the lower partial pressure ofthe water vapor 26A in the water vapor vacuum volumes 90, 92, 94 toincrease or decrease the rate of removal of water vapor 26 from the airchannels 16 to the water vapor channels 18 through the interfaces 20 ofthe dehumidification units 74, 76, 78 as H₂O (i.e., as water molecules,gaseous water vapor, liquid water, adsorbed/desorbed water molecules,absorbed/desorbed water molecules, and so forth, through the interfaces20).

For example, if more water vapor removal is desired, the lower partialpressure of the water vapor 26A in the water vapor vacuum volumes 90,92, 94 may be reduced and, conversely, if less water vapor removal isdesired, the lower partial pressure of the water vapor 26A in the watervapor vacuum volumes 90, 92, 94 may be increased. Furthermore, asdescribed above, the amount of dehumidification (i.e., water vaporremoval) may be cycled to improve the efficiency of the dehumidificationunits 74, 76, 78. More specifically, under certain operating conditions,the dehumidification units 74, 76, 78 may function more efficiently athigher rates of water vapor removal. As such, in certain embodiments,the dehumidification units 74, 76, 78 may be cycled to remove a maximumamount of water vapor from the air 14 for a period of time (e.g.,approximately 1 sec, 10 sec, 100 sec, 10 min), then to remove relativelyno water vapor from the air 14 for a period of time (e.g., approximately1 sec, 10 sec, 100 sec, 10 min), then to remove a maximum amount ofwater vapor from the air 14 for a period of time (e.g., approximately 1sec, 10 sec, 100 sec, 10 min), and so forth. In other words, thedehumidification units 74, 76, 78 may be operated at full water vaporremoval capacity for periods of time alternating with other periods oftime where no water vapor is removed. In addition, the control system 64may be configured to control start-up and shutdown sequencing of thedehumidification units 74, 76, 78.

While FIG. 8 includes a serial arrangement of multiple dehumidificationunits 12, present embodiments include other ways in which multipledehumidification units 12 may be arranged in a single HVAC system. Forexample, FIG. 9 is a schematic diagram of an HVAC system 98 having aplurality of dehumidification units 12 (i.e., a first dehumidificationunit 100, a second dehumidification unit 102, and a thirddehumidification unit 104) arranged in parallel in accordance with anembodiment of the present disclosure. Although illustrated as havingthree dehumidification units 100, 102, 104 in parallel, any number ofdehumidification units 12 may indeed be used in parallel in the HVACsystem 98. For example, in other embodiments, 2, 4, 5, 6, 7, 8, 9, 10,or even more dehumidification units 12 may be used in parallel in theHVAC system 98.

The HVAC system 98 of FIG. 9 generally functions the same as the HVACsystem 10 of FIGS. 1, 6, and 7 and the HVAC system 72 of FIG. 8. Morespecifically, as illustrated in FIG. 9, each dehumidification unit 100,102, 104 of the HVAC system 98 receives the inlet air 14A having arelatively high humidity and expels the outlet air 14B having arelatively low humidity. As illustrated, many of the components of theHVAC system 98 of FIG. 9 may be considered identical to the componentsof the HVAC system 10 of FIGS. 1, 6, and 7 and the HVAC system 72 ofFIG. 8. For example, the dehumidification units 100, 102, 104 of theHVAC system 98 of FIG. 9 may be considered identical to thedehumidification units 12 of FIGS. 1, 6, and 7 and the dehumidificationunits 74, 76, 78 of FIG. 8. In addition, the HVAC system 98 of FIG. 9also includes the condensation unit 54 that receives water vapor 26Bhaving a partial pressure just high enough to facilitate condensation,as described previously. In certain embodiments, the HVAC system 98 ofFIG. 9 may also include the reservoir 58 for temporary storage ofsaturated vapor and liquid water. However, as described previously, inother embodiments, no reservoir may be used. In either case, the liquidwater from the condensation unit 54 may be directed into the liquid pump60, within which the pressure of the liquid water from the condensationunit 54 is increased to approximately atmospheric pressure (i.e.,approximately 14.7 psia) so that the liquid water may be rejected atambient conditions.

As illustrated in FIG. 9, in certain embodiments, each dehumidificationunit 100, 102, 104 may be associated with a respective vacuum pump 106,108, 110, each of which is similar in functionality to the vacuum pump52 of FIGS. 1, 6, and 7 and the vacuum pumps 84, 86, 88 of FIG. 8.However, as opposed to the HVAC system 72 of FIG. 8, because thedehumidification units 100, 102, 104 and associated vacuum pumps 106,108, 110 are arranged in parallel, the partial pressure of water vaporin the air 14 will be approximately the same in each dehumidificationunit 100, 102, 104. As such, in general, the partial pressure of watervapor in the water vapor vacuum volumes 112, 114, 116 associated witheach respective vacuum pump 106, 108, 110 will also be approximately thesame. For example, as described previously with respect to the HVACsystem 10 of FIGS. 1, 6, and 7, the partial pressure of the water vapor26A in the water vapor vacuum volumes 112, 114, 116 may be maintained ina range of approximately 0.10-0.25 psia.

As illustrated in FIG. 9, in certain embodiments, each of the vacuumpumps 106, 108, 110 may compress the water vapor 26 and direct it into acommon manifold 118 having a substantially constant partial pressure ofwater vapor (i.e., just high enough to facilitate condensation in thecondensation unit 54). In other embodiments, the water vapor 26extracted from each successive dehumidification unit 100, 102, 104(i.e., from top to bottom) may be compressed by its respective vacuumpump 106, 108, 110 and then combined with the water vapor 26 extractedfrom the next downstream (i.e., with respect to the common manifold)dehumidification unit 100, 102, 104. For example, in other embodiments,the water vapor 26 from the first dehumidification unit 100 may becompressed by the first vacuum pump 106 and then combined with the watervapor 26 from the second dehumidification unit 102 in the second watervapor vacuum volume 114. Similarly, the water vapor 26 compressed by thesecond vacuum pump 108 may be combined with the water vapor 26 from thethird dehumidification unit 104 in the third water vapor vacuum volume116. In this embodiment, the exhaust side of each successive vacuum pump106, 108, 110 increases the partial pressure of the water vapor 26 onlyto the operating pressure of the next downstream vacuum pump 106, 108,110. For example, the first vacuum pump 106 may only increase thepressure of the water vapor 26 to approximately 0.2 psia if the partialpressure of water vapor in the second water vapor vacuum volume 114 isapproximately 0.2 psia. Similarly, the second vacuum pump 108 may onlyincrease the pressure of the water vapor 26 to approximately 0.35 psiaif the partial pressure of water vapor in the third water vapor vacuumvolume 116 is approximately 0.35 psia. In this embodiment, the watervapor 26 compressed by the third vacuum pump 110 will be directed intothe condensation unit 54 at a partial pressure of water vapor just highenough to facilitate condensation.

It should be noted that the specific embodiment illustrated in FIG. 9having a plurality of dehumidification units 100, 102, 104 arranged inparallel may be configured in various ways not illustrated in FIG. 9.For example, although illustrated as using a respective vacuum pump 106,108, 110 with each dehumidification unit 100, 102, 104, in certainembodiments, a single vacuum pump 52 may be used with multiple inletports connected to the first, second, and third water vapor vacuumvolumes 112, 114, 116. In addition, although illustrated as using asingle condensation unit 54, reservoir 58, and liquid pump 60 tocondense the water vapor 26B into a liquid state, and store and/ortransport the liquid water from the HVAC system 98, in otherembodiments, each set of dehumidification units 100, 102, 104 and vacuumpumps 106, 108, 110 may be operated independently and be associated withtheir own respective condensation units 54, reservoirs 58, and liquidpumps 60.

In addition, the control system 64 of FIG. 7 may also be used in theHVAC system 98 of FIG. 9 to control the operation of the HVAC system 98in a similar manner as described previously with respect to FIG. 7. Forexample, as described previously, the control system 64 may beconfigured to control the rate of removal of the noncondensablecomponents 30 of the water vapor 26A in the water vapor vacuum volumes112, 114, 116 by turning the vacuum pumps 106, 108, 110 (or separatevacuum pumps 62, as described previously with respect to FIGS. 6 and 7)on or off, or by modulating the rate at which the vacuum pumps 106, 108,110 (or separate vacuum pumps 62, as described previously with respectto FIGS. 6 and 7) remove the noncondensable components 30. Morespecifically, in certain embodiments, the control system 64 may receivesignals from sensors in the water vapor vacuum volumes 112, 114, 116that detect when too many noncondensable components 30 are present inthe water vapor 26A contained in the water vapor vacuum volumes 112,114, 116.

In addition, the control system 64 may modulate the lower partialpressure of the water vapor 26A in the water vapor vacuum volumes 112,114, 116 to modify the water vapor removal capacity and efficiency ratioof the dehumidification units 100, 102, 104. For example, the controlsystem 64 may receive signals from pressure sensors in the water vaporvacuum volumes 112, 114, 116, the water vapor channels 18, as well assignals generated by sensors relating to characteristics (e.g.,temperature, pressure, flow rate, relative humidity, and so forth) ofthe air 14, among other things. The control system 64 may use thisinformation to determine how to modulate the lower partial pressure ofthe water vapor 26A in the water vapor vacuum volumes 112, 114, 116 toincrease or decrease the rate of removal of water vapor 26 from the airchannels 16 to the water vapor channels 18 through the interfaces 20 ofthe dehumidification units 100, 102, 104 as H₂O (i.e., as watermolecules, gaseous water vapor, liquid water, adsorbed/desorbed watermolecules, absorbed/desorbed water molecules, and so forth, through theinterfaces 20).

For example, if more water vapor removal is desired, the lower partialpressure of the water vapor 26A in the water vapor vacuum volumes 112,114, 116 may be reduced and, conversely, if less water vapor removal isdesired, the lower partial pressure of the water vapor 26A in the watervapor vacuum volumes 112, 114, 116 may be increased. Furthermore, asdescribed above, the amount of dehumidification (i.e., water vaporremoval) may be cycled to improve the efficiency of the dehumidificationunits 100, 102, 104. More specifically, under certain operatingconditions, the dehumidification units 100, 102, 104 may function moreefficiently at higher rates of water vapor removal. As such, in certainembodiments, the dehumidification units 100, 102, 104 may be cycled toremove a maximum amount of water vapor from the air 14 for a period oftime (e.g., approximately 1 sec, 10 sec, 100 sec, 10 min), then toremove relatively no water vapor from the air 14 for a period of time(e.g., approximately 1 sec, 10 sec, 100 sec, 10 min), then to remove amaximum amount of water vapor from the air 14 for a period of time(e.g., approximately 1 sec, 10 sec, 100 sec, 10 min), and so forth. Inother words, the dehumidification units 100, 102, 104 may be operated atfull water vapor removal capacity for periods of time alternating withother periods of time where no water vapor is removed. In addition, thecontrol system 64 may be configured to control start-up and shutdownsequencing of the dehumidification units 100, 102, 104.

In addition to the serial arrangement of dehumidification units 12illustrated in FIG. 8 and the parallel arrangement of dehumidificationunits 12 illustrated in FIG. 9, multiple dehumidification units 12 maybe used in other ways. Indeed, much more complex and expansivearrangements may also be used. For example, FIG. 10 is a schematicdiagram of an HVAC system 120 having a first set 122 of dehumidificationunits 12 (i.e., a first dehumidification unit 124 and a seconddehumidification unit 126) arranged in series, and a second set 128 ofdehumidification units 12 (i.e., a third dehumidification unit 130 and afourth dehumidification unit 132) also arranged in series, with thefirst and second sets 122, 128 of dehumidification units 12 arranged inparallel in accordance with an embodiment of the present disclosure. Inother words, the first set 122 of serial first and seconddehumidification units 124, 126 are arranged in parallel with the secondset 128 of serial third and fourth dehumidification units 130, 132.

Although illustrated as having two sets 122, 128 of serialdehumidification units 12 arranged in parallel, any number of parallelpluralities of dehumidification units 12 may indeed be used in the HVACsystem 120. For example, in other embodiments, 3, 4, 5, 6, 7, 8, 9, 10,or even more parallel sets of dehumidification units 12 may be used inthe HVAC system 120. Similarly, although illustrated as having twodehumidification units 12 arranged in series within each set 122, 128 ofdehumidification units 12, any number of dehumidification units 12 mayindeed be used in series within each set 122, 128 of dehumidificationunits 12 in the HVAC system 120. For example, in other embodiments, 1,3, 4, 5, 6, 7, 8, 9, 10, or even more dehumidification units 12 may beused in series within each set 122, 128 of dehumidification units 12 inthe HVAC system 120.

All of the operating characteristics of the HVAC system 120 of FIG. 10are similar to those described previously with respect to the HVACsystems 72, 98 of FIGS. 8 and 9 (as well as the HVAC system 10 of FIGS.1, 6, and 7). For example, as illustrated, each of the dehumidificationunits 124, 126, 130, 132 may be associated with its own respectivevacuum pump 134, 136, 138, 140 (e.g., similar to the vacuum pump 52 ofFIGS. 1, 6, and 7). However, in other embodiments, one vacuum pump 52may be used for each set 122, 128 of dehumidification units 12 withmultiple inlet ports connected to the respective water vapor vacuumvolumes 142, 144, 146, 148. Indeed, in other embodiments, all of thedehumidification units 124, 126, 130, 132 may be associated with asingle vacuum pump 52 with multiple inlet ports connected to all of thewater vapor vacuum volumes 142, 144, 146, 148.

In addition, although illustrated as using a single condensation unit54, reservoir 58, and liquid pump 60 to condense the water vapor 26Binto a liquid state, and store and/or transport the liquid water fromthe HVAC system 120, in other embodiments, each set of dehumidificationunits 124, 126, 130, 132 and vacuum pumps 134, 136, 138, 140 may beoperated independently and be associated with their own respectivecondensation units 54, reservoirs 58, and liquid pumps 60. In addition,the control system 64 described previously may also be used in the HVACsystem 120 of FIG. 10 to control operation of the HVAC system 120 in asimilar manner as described previously.

The embodiments described previously with respect to FIGS. 8 through 10are slightly more complex than the embodiments described previously withrespect to FIGS. 1 through 7 inasmuch as multiple dehumidification units12 are used in series, parallel, or some combination thereof. As such,the control of pressures and temperatures of the HVAC systems 72, 98,120 of FIGS. 8 through 10 are slightly more complicated than the controlof a single dehumidification unit 12. For example, the partial pressuresin the water vapor vacuum volumes may need to be closely monitored andmodulated by the control system 64 to take into account variations intemperature and partial pressure of water vapor in the air 14 within therespective dehumidification units 12, operating pressures of adjacentwater vapor vacuum volumes and vacuum pumps (which may be cross-pipedtogether as described previously to facilitate control of pressures,flows, and so forth), among other things. In certain embodiments,variable or fixed orifices may be used to control pressures and changesin pressures in and between the dehumidification units 12. In addition,as described previously, each of the respective vacuum pumps may becontrolled to adjust the partial pressures of water vapor in the watervapor vacuum volumes to account for variations between dehumidificationunits 12.

In certain embodiments, the dehumidification unit 12 described withrespect to FIGS. 1 through 7 may be used in conjunction with one or moreevaporative cooling units 12. For example, FIG. 11 is a schematicdiagram of an HVAC system 150 having an evaporative cooling unit 152disposed upstream of the dehumidification unit 12 in accordance with anembodiment of the present disclosure. The HVAC system 150 of FIG. 11generally functions the same as the HVAC system 10 of FIGS. 1, 6, and 7.However, as illustrated in FIG. 11, the HVAC system 150 specificallyincludes the evaporative cooling unit 152 disposed upstream of thedehumidification unit 12. Thus, the HVAC system 150 first receives therelatively humid inlet air 14A into the evaporative cooling unit 152,instead of the dehumidification unit 12. The evaporative cooling unit152 reduces the temperature of the relatively humid inlet air 14A andexpels cooler (but still relatively humid) air 14B, which is directedinto the dehumidification unit 12 via a duct 154. As describedpreviously, the cooler (but still relatively humid) air 14B is thendehumidified in the dehumidification unit 12 and expelled as relativelydry air 14C into the conditioned space.

The evaporative cooling unit 152 of FIG. 11 may either be a directevaporative cooling unit or an indirect evaporative cooling unit. Inother words, when the evaporative cooling unit 152 uses directevaporative cooling techniques, a relatively cool and moist media 156(e.g., relatively cool water) is directly added to the relatively humidinlet air 14A. However, when the evaporative cooling unit 152 usesindirect evaporative cooling techniques, the relatively humid air 14Amay, for example, flow across one side of a plate of a heat exchangerwhile the relatively cool and moist media 156 flows across another sideof the plate of the heat exchanger. In other words, generally speaking,some of the relatively cool moisture from the relatively cool and moistmedia 156 is indirectly added to the relatively humid air 14A. Whetherdirect or indirect evaporative cooling techniques are used in theevaporative cooling unit 152 affects the rate of humidity removal andtemperature reduction of the air 14 that flows through the HVAC system150 of FIG. 11. In general, however, the evaporative cooling unit 152 ofFIG. 11 initially cools the air 14 to a temperature as low as possiblefor the particular application, and the dehumidification unit 12 lowersthe humidity ratio at approximately constant temperature.

As illustrated, many of the components of the HVAC system 150 of FIG. 11may be considered identical to the components of the HVAC system 10 ofFIGS. 1, 6, and 7. For example, as described previously, HVAC system 150of FIG. 11 includes the condensation unit 54 that receives water vapor26B having a partial pressure just high enough to facilitatecondensation, as described previously. In certain embodiments, the HVACsystem 150 of FIG. 11 may also include the reservoir 58 for temporarystorage of saturated vapor and liquid water. However, as describedpreviously, in other embodiments, no reservoir may be used. In eithercase, the liquid water from the condensation unit 54 may be directedinto the liquid pump 60, within which the pressure of the liquid waterfrom the condensation unit 54 is increased to approximately atmosphericpressure (i.e., approximately 14.7 psia) so that the liquid water may berejected at ambient conditions.

In addition, the control system 64 of FIG. 7 may also be used in theHVAC system 150 of FIG. 11 to control the operation of the HVAC system150 in a similar manner as described previously with respect to FIG. 7.For example, as described previously, the control system 64 may beconfigured to control the rate of removal of the noncondensablecomponents 30 of the water vapor 26A in the water vapor vacuum volume 28by turning the vacuum pump 52 (or separate vacuum pump 62) on or off, orby modulating the rate at which the vacuum pump 52 (or separate vacuumpump 62) removes the noncondensable components 30. More specifically, incertain embodiments, the control system 64 may receive signals fromsensors in the water vapor vacuum volume 28 that detect when too manynoncondensable components 30 are present in the water vapor 26Acontained in the water vapor vacuum volume 28.

In addition, the control system 64 may modulate the lower partialpressure of the water vapor 26A in the water vapor vacuum volume 28 tomodify the water vapor removal capacity and efficiency ratio of thedehumidification unit 12. For example, the control system 64 may receivesignals from pressure sensors in the water vapor vacuum volume 28, thewater vapor channels 18, as well as signals generated by sensorsrelating to characteristics (e.g., temperature, pressure, flow rate,relative humidity, and so forth) of the air 14 in the evaporativecooling unit 152, the dehumidification unit 12, or both, among otherthings.

The control system 64 may use this information to determine how tomodulate the lower partial pressure of the water vapor 26A in the watervapor vacuum volume 28 to increase or decrease the rate of removal ofwater vapor 26 from the air channels 16 to the water vapor channels 18through the interfaces 20 of the dehumidification unit 12 as H₂O (i.e.,as water molecules, gaseous water vapor, liquid water, adsorbed/desorbedwater molecules, absorbed/desorbed water molecules, and so forth,through the interfaces 20). For example, if more water vapor removal isdesired, the lower partial pressure of the water vapor 26A in the watervapor vacuum volume 28 may be reduced and, conversely, if less watervapor removal is desired, the lower partial pressure of the water vapor26A in the water vapor vacuum volume 28 may be increased. Furthermore,as described above, the amount of dehumidification (i.e., water vaporremoval) may be cycled to improve the efficiency of the dehumidificationunit 12. More specifically, under certain operating conditions, thedehumidification unit 12 may function more efficiently at higher ratesof water vapor removal. As such, in certain embodiments, thedehumidification unit 12 may be cycled to remove a maximum amount ofwater vapor from the air 14 for a period of time (e.g., approximately 1sec, 10 sec, 100 sec, 10 min), then to remove relatively no water vaporfrom the air 14 for a v (e.g., approximately 1 sec, 10 sec, 100 sec, 10min), then to remove a maximum amount of water vapor from the air 14 fora period of time (e.g., approximately 1 sec, 10 sec, 100 sec, 10 min),and so forth. In other words, the dehumidification unit 12 may beoperated at full water vapor removal capacity for periods of timealternating with other periods of time where no water vapor is removed.

Furthermore, the control system 64 may also be configured to controloperation of the evaporative cooling unit 152. For example, the controlsystem 64 may selectively modulate how much (direct or indirect)evaporative cooling occurs in the evaporative cooling unit 152. As anexample, valves may be actuated to control the flow rate of therelatively cool and moist media 156 through the evaporative cooling unit152, thereby directly affecting the amount of (direct or indirect)evaporative cooling in the evaporative cooling unit 152. In addition,operation of the evaporative cooling unit 152 and the dehumidificationunit 12 may be controlled simultaneously. Furthermore, the controlsystem 64 may be configured to control start-up and shutdown sequencingof the evaporative cooling unit 152 and the dehumidification unit 12.

FIGS. 12A and 12B are psychrometric charts 158, 160 of the temperatureand the humidity ratio of the air 14 flowing through the evaporativecooling unit 152 and the dehumidification unit 12 of FIG. 11 inaccordance with an embodiment of the present disclosure. Morespecifically, FIG. 12A is the psychrometric chart 158 of the temperatureand the humidity ratio of the air 14 flowing through a directevaporative cooling unit 152 and the dehumidification unit 12 of FIG. 11in accordance with an embodiment of the present disclosure, and FIG. 12Bis the psychrometric chart 160 of the temperature and the humidity ratioof the air 14 flowing through an indirect evaporative cooling unit 152and the dehumidification unit 12 of FIG. 11 in accordance with anembodiment of the present disclosure. In particular, in each chart 158,160, the x-axis 162 corresponds to the temperature of the air 14 flowingthrough the evaporative cooling unit 152 and the dehumidification unit12 of FIG. 11, the y-axis 164 corresponds to the humidity ratio of theair 14 flowing through the evaporative cooling unit 152 and thedehumidification unit 12 of FIG. 11, and the curve 166 represents thewater vapor saturation curve for a given relative humidity of the air 14flowing through the evaporative cooling unit 152 and thedehumidification unit 12 of FIG. 11.

As illustrated by line 168 in FIG. 12A, because the relatively cool andmoist media 156 is directly introduced into the air 14 flowing thoughthe direct evaporative cooling unit 152, the humidity ratio of the air14B (i.e., point 170) out of the direct evaporative cooling unit 152 issubstantially higher than the humidity ratio of the inlet air 14A (i.e.,point 172) into the direct evaporative cooling unit 152. However, thetemperature of the air 14B (i.e., point 170) out of the directevaporative cooling unit 152 is substantially lower than the temperatureof the inlet air 14A (i.e., point 172) into the evaporative cooling unit152. As illustrated by line 174 of FIG. 12A, because water vapor 26 isremoved from the air 14B flowing through the dehumidification unit 12,the humidity ratio of the outlet air 14C (i.e., point 176) from thedehumidification unit 12 is lower than the humidity ratio of the air 14B(i.e., point 170) into the dehumidification unit 12, while thetemperature of the outlet air 14C and the air 14B are substantially thesame. Indeed, the direct evaporative cooling unit 152 humidifies andcools the air 14, while the dehumidification unit 12 subsequentlydehumidifies the air 14 at substantially constant temperature.

As illustrated by line 178 in FIG. 12B, because the relatively cool andmoist media 156 indirectly cools the air 14 flowing through the indirectevaporative cooling unit 152, the humidity ratio of the air 14B (i.e.,point 180) out of the indirect evaporative cooling unit 152 issubstantially the same as the humidity ratio of the inlet air 14A (i.e.,point 182) into the indirect evaporative cooling unit 152. However, thetemperature of the air 14B (i.e., point 180) out of the indirectevaporative cooling unit 152 is substantially lower than the temperatureof the inlet air 14A (i.e., point 182) into the indirect evaporativecooling unit 152. As illustrated by line 184 of FIG. 12B, because watervapor 26 is removed from the air 14B flowing through thedehumidification unit 12, the humidity ratio of the outlet air 14C(i.e., point 186) from the dehumidification unit 12 is lower than thehumidity ratio of the air 14B (i.e., point 180) into thedehumidification unit 12, while the temperature of the outlet air 14Cand the air 14B are substantially the same. Indeed, the indirectevaporative cooling unit 152 cools (without substantially humidifying)the air 14, while the dehumidification unit 12 subsequently dehumidifiesthe air 14 at substantially constant temperature.

As described previously, the control system 64 of FIG. 11 may beconfigured to control the operation of the evaporative cooling unit 152and the dehumidification unit 12. For example, the control system 64 maybe configured to adjust where points 170, 172, 176 and points 180, 182,186 of the air 14 fall in the psychrometric charts 158, 160 of FIGS. 12Aand 12B when direct and indirect evaporative cooling techniques,respectively, are used in the evaporative cooling unit 152 of FIG. 11.

FIG. 13 is a schematic diagram of an HVAC system 188 having theevaporative cooling unit 152 disposed downstream of the dehumidificationunit 12 in accordance with an embodiment of the present disclosure. TheHVAC system 188 of FIG. 13 generally functions the same as the HVACsystem 10 of FIGS. 1, 6, and 7 and the HVAC system 150 of FIG. 11.However, as illustrated in FIG. 13, the HVAC system 188 first receivesthe relatively humid inlet air 14A into the dehumidification unit 12. Asdescribed previously, the relatively humid inlet air 14A is firstdehumidified in the dehumidification unit 12 and expelled as relativelydry air 14B into the duct 154. The evaporative cooling unit 152 thenreduces the temperature of the dry air 14B and expels cooler dry air 14Cinto the conditioned space.

As described previously with respect to FIG. 11, the evaporative coolingunit 152 of FIG. 13 may either be a direct evaporative cooling unit oran indirect evaporative cooling unit. In other words, when theevaporative cooling unit 152 uses direct evaporative cooling techniques,the relatively cool and moist media 156 (e.g., relatively cool water) isdirectly added to the relatively dry air 14B in the duct 154. However,when the evaporative cooling unit 152 uses indirect evaporative coolingtechniques, the relatively dry air 14B may, for example, flow across oneside of a plate of a heat exchanger while the relatively cool and moistmedia 156 flows across another side of the plate of the heat exchanger.In other words, generally speaking, some of the relatively cool moisturefrom the relatively cool and moist media 156 is indirectly added to therelatively dry air 14B in the duct 154. Whether direct or indirectevaporative cooling techniques are used in the evaporative cooling unit152 affects the rate of humidity removal and temperature reduction ofthe air 14 that flows through the HVAC system 188 of FIG. 13. Ingeneral, however, the dehumidification unit 12 initially lowers thehumidity ratio at approximately constant temperature, and theevaporative cooling unit 152 cools the air 14 to a temperature as low aspossible for the particular application.

As illustrated, many of the components of the HVAC system 188 of FIG. 13may be considered identical to the components of the HVAC system 10 ofFIGS. 1, 6, and 7 and the HVAC system 150 of FIG. 11. For example, asdescribed previously, HVAC system 188 of FIG. 13 includes thecondensation unit 54 that receives water vapor 26B having a partialpressure just high enough to facilitate condensation, as describedpreviously. In certain embodiments, the HVAC system 188 of FIG. 13 mayalso include the reservoir 58 for temporary storage of saturated vaporand liquid water. However, as described previously, in otherembodiments, no reservoir may be used. In either case, the liquid waterfrom the condensation unit 54 may be directed into the liquid pump 60,within which the pressure of the liquid water from the condensation unit54 is increased to approximately atmospheric pressure (i.e.,approximately 14.7 psia) so that the liquid water may be rejected atambient conditions.

In addition, the control system 64 of FIGS. 7 and 11 may also be used inthe HVAC system 188 of FIG. 13 to control the operation of the HVACsystem 188 in a similar manner as described previously with respect toFIGS. 7 and 11. For example, as described previously, the control system64 may be configured to control the rate of removal of thenoncondensable components 30 of the water vapor 26A in the water vaporvacuum volume 28 by turning the vacuum pump 52 (or separate vacuum pump62) on or off, or by modulating the rate at which the vacuum pump 52 (orseparate vacuum pump 62) removes the noncondensable components 30. Morespecifically, in certain embodiments, the control system 64 may receivesignals from sensors in the water vapor vacuum volume 28 that detectwhen too many noncondensable components 30 are present in the watervapor 26A contained in the water vapor vacuum volume 28.

In addition, the control system 64 may modulate the lower partialpressure of the water vapor 26A in the water vapor vacuum volume 28 tomodify the water vapor removal capacity and efficiency ratio of thedehumidification unit 12. For example, the control system 64 may receivesignals from pressure sensors in the water vapor vacuum volume 28, thewater vapor channels 18, as well as signals generated by sensorsrelating to characteristics (e.g., temperature, pressure, flow rate,relative humidity, and so forth) of the air 14 in the dehumidificationunit 12, the evaporative cooling unit 152, or both, among other things.

The control system 64 may use this information to determine how tomodulate the lower partial pressure of the water vapor 26A in the watervapor vacuum volume 28 to increase or decrease the rate of removal ofwater vapor 26 from the air channels 16 to the water vapor channels 18through the interfaces 20 of the dehumidification unit 12 as H₂O (i.e.,as water molecules, gaseous water vapor, liquid water, adsorbed/desorbedwater molecules, absorbed/desorbed water molecules, and so forth,through the interfaces 20). For example, if more water vapor removal isdesired, the lower partial pressure of the water vapor 26A in the watervapor vacuum volume 28 may be reduced and, conversely, if less watervapor removal is desired, the lower partial pressure of the water vapor26A in the water vapor vacuum volume 28 may be increased. Furthermore,as described above, the amount of dehumidification (i.e., water vaporremoval) may be cycled to improve the efficiency of the dehumidificationunit 12. More specifically, under certain operating conditions, thedehumidification unit 12 may function more efficiently at higher ratesof water vapor removal. As such, in certain embodiments, thedehumidification unit 12 may be cycled to remove a maximum amount ofwater vapor from the air 14 for a period of time (e.g., approximately 1sec, 10 sec, 100 sec, 10 min), then to remove relatively no water vaporfrom the air 14 for a period of time (e.g., approximately 1 sec, 10 sec,100 sec, 10 min), then to remove a maximum amount of water vapor fromthe air 14 for a period of time (e.g., approximately 1 sec, 10 sec, 100sec, 10 min), and so forth. In other words, the dehumidification unit 12may be operated at full water vapor removal capacity for periods of timealternating with other periods of time where no water vapor is removed.

Furthermore, the control system 64 may also be configured to controloperation of the evaporative cooling unit 152. For example, the controlsystem 64 may selectively modulate how much (direct or indirect)evaporative cooling occurs in the evaporating cooling unit 152. As anexample, valves may be actuated to control the flow rate of therelatively cool and moist media 156 through the evaporative cooling unit152, thereby directly affecting the amount of (direct or indirect)evaporative cooling in the evaporative cooling unit 152. In addition,operation of the dehumidification unit 12 and the evaporative coolingunit 152 may be controlled simultaneously. Furthermore, the controlsystem 64 may be configured to control start-up and shutdown sequencingof the dehumidification unit 12 and the evaporative cooling unit 152.

FIGS. 14A and 14B are psychrometric charts 190, 192 of the temperatureand the humidity ratio of the air 14 flowing through thedehumidification unit 12 and the evaporative cooling unit 152 of FIG. 13in accordance with an embodiment of the present disclosure. Morespecifically, FIG. 14A is the psychrometric chart 190 of the temperatureand the humidity ratio of the air 14 flowing through thedehumidification unit 12 and a direct evaporative cooling unit 152 ofFIG. 13 in accordance with an embodiment of the present disclosure, andFIG. 14B is the psychrometric chart 192 of the temperature and thehumidity ratio of the air 14 flowing through the dehumidification unit12 and an indirect evaporative cooling unit 152 of FIG. 13 in accordancewith an embodiment of the present disclosure. In particular, asdescribed previously with respect to FIGS. 12A and 12B, the x-axis 162corresponds to the temperature of the air 14 flowing through thedehumidification unit 12 and the evaporative cooling unit 152 of FIG.13, the y-axis 164 corresponds to the humidity ratio of the air 14flowing through the dehumidification unit 12 and the evaporative coolingunit 152 of FIG. 13, and the curve 166 represents the water vaporsaturation curve for a given relative humidity of the air 14 flowingthrough the dehumidification unit 12 and the evaporative cooling unit152 of FIG. 13.

As illustrated by line 194 in FIG. 14A, because water vapor 26 isremoved from the relatively humid inlet air 14A flowing through thedehumidification unit 12, the humidity ratio of the relatively dry air14B (i.e., point 196) from the dehumidification unit 12 is lower thanthe humidity ratio of the relatively humid inlet air 14A (i.e., point198) into the dehumidification unit 12, while the temperature of therelatively dry air 14B and the relatively humid inlet air 14A aresubstantially the same. As illustrated by line 200 of FIG. 14A, becausethe relatively cool and moist media 156 is directly introduced into therelatively dry air 14B flowing through the direct evaporative coolingunit 152, the humidity ratio of the outlet air 14C (i.e., point 202)from the direct evaporative cooling unit 152 is substantially higherthan the humidity ratio of the relatively dry air 14B (i.e., point 196)into the direct evaporative cooling unit 152. However, the temperatureof the outlet air 14C (i.e., point 202) from the direct evaporativecooling unit 152 is substantially lower than the temperature of therelatively dry air 14B (i.e., point 196) into the direct evaporativecooling unit 152. Indeed, the dehumidification unit 12 dehumidifies theair 14 at substantially constant temperature, while the directevaporative cooling unit 152 subsequently humidifies and cools the air14.

As illustrated by line 204 in FIG. 14B, because water vapor 26 isremoved from the relatively humid inlet air 14A flowing through thedehumidification unit 12, the humidity ratio of the relatively dry air14B (i.e., point 206) from the dehumidification unit 12 is lower thanthe humidity ratio of the relatively humid inlet air 14A (i.e., point208) into the dehumidification unit 12, while the temperature of therelatively dry air 14B and the relatively humid inlet air 14A aresubstantially the same. As illustrated by line 210 of FIG. 14B, becausethe relatively cool and moist media 156 indirectly cools the relativelydry air 14B flowing though the indirect evaporative cooling unit 152,the humidity ratio of the outlet air 14C (i.e., point 212) from theindirect evaporative cooling unit 152 is substantially the same as thehumidity ratio of the relatively dry air 14B (i.e., point 206) into theindirect evaporative cooling unit 152. However, the temperature of theoutlet air 14C (i.e., point 212) from the indirect evaporative coolingunit 152 is substantially lower than the temperature of the relativelydry air 14B (i.e., point 206) into the indirect evaporative cooling unit152. Indeed, the dehumidification unit 12 dehumidifies the air 14 atsubstantially constant temperature, while the indirect evaporativecooling unit 152 cools (without substantially humidifying) the air 14.

As described previously, the control system 64 of FIG. 13 may beconfigured to control the operation of the dehumidification unit 12 andthe evaporative cooling unit 152. For example, the control system 64 maybe configured to adjust where points 196, 198, 202 and points 206, 208,212 of the air 14 fall in the psychrometric charts 190, 192 of FIGS. 14Aand 14B when direct and indirect evaporative cooling techniques,respectively, are used in the evaporative cooling unit 152 of FIG. 13.

The embodiments of the HVAC systems 150, 188 of FIGS. 11 and 13 are notthe only ways in which dehumidification units 12 may be combined withevaporative cooling units 152. More specifically, whereas FIGS. 11 and13 illustrate the use of a single dehumidification unit 12 and a singleevaporative cooling unit 152 in series with each other, in otherembodiments, any number of dehumidification units 12 and evaporativecooling units 152 may be used in series with each other. As anotherexample, in one embodiment, a first dehumidification unit 12 may befollowed by a first evaporative cooling unit 152, which is in turnfollowed by a second dehumidification unit 12, which is in turn followedby a second evaporative cooling unit 152, and so forth. However, anynumber of dehumidification units 12 and evaporative cooling units 152may indeed be used in series with each other, wherein the air 14 exitingeach unit 12, 152 is directed into the next downstream unit 12, 152 inthe series (except from the last unit 12, 152 in the series, from whichthe air 14 is expelled into the conditioned space). In other words, theair 14 exiting each dehumidification unit 12 in the series is directedinto a downstream evaporative cooling unit 152 (or to the conditionedspace, if it is the last unit in the series), and the air 14 exitingeach evaporative cooling unit 152 in the series is directed into adownstream dehumidification unit 12 (or to the conditioned space, if itis the last unit in the series). As such, the temperature of the air 14may be successively lowered in each evaporative cooling unit 152 betweendehumidification units 12 in the series, and the humidity ratio of theair 14 may be successively lowered in each dehumidification unit 12between evaporative cooling units 152 in the series. This process may becontinued within any number of dehumidification units 12 and evaporativecooling units 152 (e.g., 2, 3, 4, 5, 6, 7, 8, 9, 10, or more units 12and/or units 152) until the desired final temperature and humidity ratioconditions of the air 14 are achieved. In one embodiment, eachdehumidification unit 12 may be combined with a correspondingevaporative cooling unit 152. In another embodiment, more than onedehumidification unit 12 may be combined with a single evaporativecooling unit 152, or vice versa. The combinations may include thedehumidification unit 12 upstream of the evaporative cooling unit 152,or downstream of the evaporative cooling unit 152.

FIGS. 15A and 15B are psychrometric charts 214, 216 of the temperatureand the humidity ratio of the air 14 flowing through a plurality ofdehumidification units 12 and a plurality of evaporative cooling units152 in accordance with an embodiment of the present disclosure. Morespecifically, FIG. 15A is a psychrometric chart 214 of the temperatureand the humidity ratio of the air 14 flowing through a plurality ofdehumidification units 12 and a plurality of direct evaporative coolingunits 152 in accordance with an embodiment of the present disclosure,and FIG. 15B is a psychrometric chart 216 of the temperature and thehumidity ratio of the air 14 flowing through a plurality ofdehumidification units 12 and a plurality of indirect evaporativecooling units 152 in accordance with an embodiment of the presentdisclosure. In particular, in each chart 214, 216, the x-axis 162corresponds to the temperature of the air 14 flowing through theplurality of dehumidification units 12 and the plurality of evaporativecooling units 152, the y-axis 164 corresponds to the humidity ratio ofthe air 14 flowing through the plurality of dehumidification units 12and the plurality of evaporative cooling units 152, and the curve 166represents the water vapor saturation curve for a given relativehumidity of the air 14 flowing through the plurality of dehumidificationunits 12 and the plurality of evaporative cooling units 152.

As illustrated by lines 218 in FIG. 15A, because water vapor 26 isremoved from relatively humid air 14 flowing through each of theplurality of dehumidification units 12, the humidity ratio of the air 14substantially decreases while the temperature of the air 14 remainssubstantially the same in each of the plurality of dehumidificationunits 12. As illustrated by lines 220 in FIG. 15A, because therelatively cool and moist media 156 is directly introduced into therelatively dry air 14 flowing though each of the direct evaporativecooling units 152, the humidity ratio of the air 14 increases while thetemperature of the air 14 substantially decreases in each of theplurality of direct evaporative cooling units 152. In other words, eachof the plurality of dehumidification units 12 successively dehumidifiesthe air 14 at substantially constant temperature, while each of theplurality of direct evaporative cooling units 152 successivelyhumidifies and cools the air 14 until the desired final conditions oftemperature and humidity ratio are achieved. More specifically, asillustrated in FIG. 15A, the lines 218, 220 generally form a “stepfunction” progression from the initial conditions of temperature andhumidity ratio of the inlet air 14 (i.e., point 222) to the finalconditions of temperature and humidity ratio of the outlet air 14 (i.e.,point 224).

As illustrated by lines 226 in FIG. 15B, because water vapor 26 isremoved from relatively humid air 14 flowing through each of theplurality of dehumidification units 12, the humidity ratio of the air 14substantially decreases while the temperature of the air 14 remainssubstantially the same in each of the plurality of dehumidificationunits 12. As illustrated by lines 228 in FIG. 15B, because therelatively cool and moist media 156 indirectly interacts with therelatively dry air 14 flowing though each of the indirect evaporativecooling units 152, the humidity ratio of the air 14 remainssubstantially the same while the temperature of the air 14 substantiallydecreases in each of the plurality of indirect evaporative cooling units152. In other words, each of the plurality of dehumidification units 12successively dehumidifies the air 14 at substantially constanttemperature, while each of the plurality of indirect evaporative coolingunits 152 successively cools the air 14 at substantially constanthumidity ratio until the desired final conditions of temperature andhumidity ratio are achieved. More specifically, as illustrated in FIG.15B, the lines 226, 228 generally form a “sawtooth” progression from theinitial conditions of temperature and humidity ratio of the inlet air 14(i.e., point 230) to the final conditions of temperature and humidityratio of the outlet air 14 (i.e., point 232).

Because evaporative cooling units 152 are used between dehumidificationunits 12, each dehumidification unit 12 receives air 14 that is coolerand at a lower partial pressure of water vapor than the upstreamdehumidification units 12. As such, each of the dehumidification units12 operates at substantially different operating conditions.Accordingly, the control system 64 may be used to modulate the operatingparameters (e.g., the partial pressures of water vapor in the watervapor vacuum volumes 28, among other things) of the dehumidificationunits 12 to take into account the variations between dehumidificationunits 12. Similarly, because dehumidification units 12 are used betweenevaporative cooling units 152, each evaporative cooling unit 152 alsoreceives air 14 that is cooler and at a lower partial pressure of watervapor than the upstream evaporative cooling units 152. As such, each ofthe evaporative cooling units 152 also operates at substantiallydifferent operating conditions. Accordingly, the control system 64 mayalso be used to modulate the operating parameters (e.g., the flow ratesof the relatively cool and moist media 156, among other things) of theevaporative cooling units 152 to take into account the variationsbetween evaporative cooling units 152. In addition, the control system64 may also simultaneously coordinate operation of the plurality ofdehumidification units 12 and the plurality of evaporative cooling units152 to take the variations into account.

The evaporative cooling units 152 of FIGS. 11 and 13 not only serve tolower the temperature of the air 14, but also serve to clean the air 14by, for example, passing the air 14 through a moist, fibrous mat. Inaddition, the dehumidification units 12 and the evaporative coolingunits 14 may be operated at variable speeds or fixed speeds for optimaloperation between different initial temperature and humidity conditions(i.e., operating points 222 and 230 in FIGS. 15A and 15B, respectively)and the final temperature and humidity conditions (i.e., operatingpoints 224 and 232 in FIGS. 15A and 15B, respectively). Furthermore, theevaporative cooling units 152 are relatively low-energy units, therebyminimizing overall operating costs.

In addition to the embodiments described previously, in otherembodiments, one or more of the dehumidification unit 12 describedherein may be used in conjunction with one or more mechanical coolingunits. For example, FIG. 16 is a schematic diagram of an HVAC system 234having a mechanical cooling unit 236 disposed downstream of thedehumidification unit 12 in accordance with an embodiment of the presentdisclosure, and FIG. 17 is a schematic diagram of an HVAC system 238having the mechanical cooling unit 236 of FIG. 16 disposed upstream ofthe dehumidification unit 12 in accordance with an embodiment of thepresent disclosure. In each of these embodiments, the mechanical coolingunit 236 may include components typical for mechanical cooling units 236such as a compressor 240 (e.g., a variable speed compressor), acondenser 242, and so forth. A refrigerant is recycled through thecomponents to cool the air received from the dehumidification unit 12(i.e., FIG. 16) or the air delivered to the dehumidification unit (i.e.,FIG. 17) to deliver non-latent, sensible compression cooling to the air.Although the embodiments illustrated in FIGS. 16 and 17 illustrate theuse of one dehumidification unit 12 and one mechanical cooling unit 236in series, in other embodiments, any number of the dehumidificationunits 12 and mechanical cooling units 236 may be used in series,parallel, or some combination thereof (similar to the embodimentsdescribed previously). In certain embodiments, one or moredehumidification units 12 may be retrofitted into existing HVAC systemshave mechanical cooling units 236.

In addition, in certain embodiments, the dehumidification units 12described herein may be used as distributed dehumidification units 12that may, for example, be portable and may be retrofitted into existingHVAC systems. For example, FIG. 18 is a schematic diagram of an HVACsystem 244 using mini-dehumidification units 246 in accordance with anembodiment of the present disclosure, wherein the mini-dehumidificationunits 246 include all of the functionality of the dehumidification units12 described previously. As illustrated, the mini-dehumidification units246 may be connected to existing ducts 248 of the components 250 of theHVAC system 244 to improve the dehumidification capabilities of the HVACsystem 244. In certain embodiments, fans 252 (e.g., variable speed fans)may be used to blow air from the existing HVAC components 250 of theHVAC system 244 into the mini-dehumidification units 246. Themini-dehumidification units 246 may be sized to facilitate coordinationwith standard components of existing HVAC systems.

In addition, in certain embodiments, the dehumidification units 12described herein may be modified slightly to use them as enthalpyrecovery ventilators (ERVs). For example, in a first ERV embodiment,relatively high humidity air and relatively low humidity air may flow ina counterflow arrangement on opposite sides of an interface 20 (e.g., awater vapor permeable membrane) as described previously. Alternatively,in a second ERV embodiment, relatively high humidity air and relativelylow humidity air may flow in a parallel flow arrangement on oppositesides of an interface 20 as described previously. In both of theseembodiments, the vacuum pump 52 described previously may not be used.Rather, both humidity and sensible heat may be recovered throughtransfer between the relatively high humidity air and the relatively lowhumidity air through the interface 20. In addition, both of the ERVembodiments may have sections inserted between the interface 20 toincrease heat transfer between the relatively high humidity air and therelatively low humidity air on opposite sides of the interface 20.

In addition, the ERV embodiments described previously may be combinedwith other stages to improve the overall performance of the system. Forexample, in certain embodiments, a single section membranedehumidification unit 12 with associated vacuum pump 52 and condensationunit 54 (e.g., such as the HVAC system 10 of FIGS. 1, 6, and 7) may beconnected upstream or downstream (or both) of one of the ERVembodiments. In other embodiments, a multistage membranedehumidification unit 12 with associated vacuum pump 52 and condensationunit 54 (e.g., such as the HVAC systems 72, 98, 120 of FIGS. 8 through10) may be connected upstream or downstream (or both) of one of the ERVembodiments. In other embodiments, a single stage or multi-stagedehumidification unit 12 with associated vacuum pump 52, condensationunit 54, and one or more evaporative cooling units 152 (e.g., such asthe HVAC systems 150, 188 of FIGS. 11 and 13) may be connected upstreamor downstream (or both) of one of the ERV embodiments. In otherembodiments, a single stage or multi-stage membrane dehumidificationunit 12 with sensible compression cooling (e.g., such as the HVACsystems 234, 238 of FIGS. 16 and 17) may be connected upstream ordownstream (or both) of one of the ERV embodiments.

In addition, in other embodiments, the vacuum pump 52 describedpreviously may be a multi-stage vacuum pump. This multi-stage vacuumpump 52 will make the improved efficiency of the multi-stage HVACsystems 72, 98, 120 of FIGS. 8 through 10 and the evaporative coolingHVAC systems 150, 188 of FIGS. 11 and 13 more readily achievable inpractice. In certain embodiments, the multi-stage vacuum pump 52 may bea turbine type vacuum pump that has multiple inlets, such that themulti-stage vacuum pump 52 may suction water vapor 26A into themulti-stage vacuum pump 52 at increasing pressures in a continuous flowprocess. The flow rate increases as the pressure increases, becauseadditional water vapor 26A is sucked into the multi-stage vacuum pump52. The multi-stage vacuum pump 52 may be combined with the multi-stagedehumidification units 12 (e.g., dehumidification units 74, 76, 78 ofFIG. 8, dehumidification units 100, 102, 104 of FIG. 9, ordehumidification units 124, 126, 130, 132 of FIG. 10). The high pressureend of the turbine in the multi-stage vacuum pump 52 removes moisturefrom the highest moisture stage, while the lowest pressure stage of theturbine of the multi-stage vacuum pump 52 is coupled to the lowestmoisture stage. The controller 64 described previously may be used tocontrol the flow into the various stages. In addition, in certainembodiments, two or more turbines may operate in parallel so that theturbines can have more pressure difference between inlets than may existbetween sequential stages. The multi-stage vacuum pump 52 may also becombined with the dehumidification units 12 and evaporative coolingunits 152 of FIGS. 11 and 13. In addition, the multi-stage vacuum pump52 may also be combined with a multi-stage dehumidifier that is followedby a compression cooler to provide sensible cooling (e.g., such as theHVAC systems 234, 238 of FIGS. 16 and 17).

In addition, in certain embodiments, the condensation unit 54 describedpreviously may be replaced with a membrane module, which includes one ormore interfaces 20 (e.g., water vapor permeable membranes) similar tothose used in the dehumidification units 12 described herein. In theseembodiments, the water vapor 26B from the vacuum pump 52 may be directedinto the membrane module, where part of the water vapor 26B passesthrough the interfaces 20 and is rejected to atmosphere, whereas othercomponents in the water vapor 26B are substantially blocked from flowinginto a water vapor channel of the membrane module. In addition, in otherembodiments, this membrane module may be used in combination with thecondensation unit 54.

Turning now to FIG. 19, the figure is a schematic diagram of an HVACsystem 300 including a multi-stage vacuum pump 302 coupled to multiplecooling and dehumidification stages 304 and 306. Although illustrated ashaving two stages 304 and 306 disposed in series, any number of coolingand dehumidification stages may be used. For example, in otherembodiments, 2, 4, 5, 6, 7, 8, 9, 10, or even more dehumidification andcooling stages may be used in series in the HVAC system 300. Asillustrated, each stage 304 and 306 includes the evaporative coolingunit 152 disposed upstream of the dehumidification unit 12, inaccordance with an embodiment of the present disclosure. The HVAC system300 of FIG. 19 generally functions the same as the HVAC system 10 ofFIGS. 1, 6, and 7 and the HVAC system 150 of FIG. 11. However, asillustrated in FIG. 19, the HVAC system 300 first receives therelatively humid inlet air 14A into the evaporative cooling unit 152.Accordingly, the relatively humid inlet air 14A may first be cooled. Theevaporative cooling unit 152 then expels the cooler air 14B into theduct 154. The dehumidification unit 12 then dries the cooler air, andexpels cooler dry air 14C into the conditioned space, approximate to asection 308.

As illustrated, the section 308 of the HVAC system 300 may include onemore cooling and dehumidification stages, each stage including theevaporative cooling unit 152 disposed upstream of the dehumidificationunit 12. Indeed, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more cooling anddehumidification stages may be disposed in the section 308 of the HVACsystem. The stages found in section 308 may then further cool anddehumidify the air 14C, resulting in a cooler, drier air 14D. In thedepicted embodiment, the air 14D may then be further processed by thefinal stage 306. That is, the air 14D may first be cooled into a coolerair 14E by the final stage, and then the air 14E may be dehumidified,thus producing a cooler, low humidity air 14F. By providing for multiplestages (each subsequent stage further cooling and dehumidifying theinitial air 14A), a cooler, low humidity air 14F may be produced in amore efficient manner. For, example, the single multi-stage vacuum pump302 may be used to drive the conversion between the air 14A and the air14F.

In certain embodiments, the multi-stage vacuum pump 302 includes acentrifugal pump (e.g., turbine type vacuum pump) that has multipleinlets 310 and 312. While two inlets 310 and 312 are depicted, 3, 4, 5,6, 7, 8, 9, 10 or more inlets may be used. As the water vapor passesthrough the turbine pump 302, the turbine pump 302 can suction vapor atincreasing pressures in a continuous flow process. The flow rateincreases as the pressure increases because additional vapor is suckedinto the turbine pump 302. In other embodiment, the multi-stage vacuumpump may be combined with a multi-stage dehumidifier and the highpressure end of the turbine pump 302 may remove moisture from thehighest moisture stage of the multi-stage dehumidifier, while the lowestpressure stage of the turbine is coupled to the lowest moisture stage ofthe dehumidifier. Additionally, while each of the stages 304 and 306 aredepicted as having a single evaporative cooling unit 152 and a singledehumidification unit 12, other stages may have multiple evaporativecooling units 152 and/or multiple dehumidification units 12. Further, inother embodiments, the evaporative cooling unit 152 may be replaced oradded to the mechanical cooling unit 236 described in FIG. 16.

As described previously with respect to FIG. 13, each evaporativecooling unit 152 of FIG. 19 may either be a direct evaporative coolingunit or an indirect evaporative cooling unit. In other words, when theevaporative cooling unit 152 uses direct evaporative cooling techniques,the relatively cool and moist media 156 (e.g., relatively cool water) isdirectly added, for example, to the relatively dry air 14B and 14E.However, when the evaporative cooling unit 152 uses indirect evaporativecooling techniques, the relatively dry air 14B and 14E may, for example,flow across one side of a plate of a heat exchanger while the relativelycool and moist media 156 flows across another side of the plate of theheat exchanger. In other words, generally speaking, some of therelatively cool moisture from the relatively cool and moist media 156 isindirectly added to the relatively dry air 14B and 14E. Whether director indirect evaporative cooling techniques are used in the evaporativecooling unit 152 affects the rate of humidity removal and temperaturereduction of the air 14 that flows through the HVAC system 300 of FIG.19. In general, however, each of the dehumidification units 12 initiallylowers the humidity ratio at approximately constant temperature, andeach of the evaporative cooling unit 152 cools the air 14 to atemperature as low as possible for the particular stage.

As illustrated, many of the components of the HVAC system 300 of FIG. 19may be considered identical to the components of the HVAC system 10 ofFIGS. 1, 6, and 7, the HVAC system 150 of FIG. 11, and the HVAC system188 of FIG. 13. For example, as described previously, the HVAC system300 of FIG. 19 includes the condensation unit 54 that receives watervapor 26A, as described previously. In certain embodiments, the HVACsystem 300 of FIG. 19 may also include the reservoir 58 for temporarystorage of saturated vapor and liquid water. However, as describedpreviously, in other embodiments, no reservoir may be used. In eithercase, the liquid water from the condensation unit 54 may be directedinto the liquid pump 60, within which the pressure of the liquid waterfrom the condensation unit 54 is increased to approximately atmosphericpressure (i.e., approximately 14.7 psia) so that the liquid water may berejected at ambient conditions. Additionally, or alternatively, a lowpressure side may include the vacuum pumps 62 useful in purgingnoncondensable components.

In certain embodiment, the HVAC system 300 may provide for increasedreliability and redundancy by using bypass conduits and valves, such asthe depicted conduits 314, 316 (e.g., bypass ducts) and bypass valve318. In these embodiments, the bypass conduits 314, 316 and valve 318may bypass certain cooling and dehumidification stages. For example, ifit is desired to perform maintenance on the stages disposed in section308, the bypass valve may be actuated and air 14C may be directed toenter the final stage 306 rather than the stages disposed in section308. Accordingly, components of the HVAC system 300 may be maintained orreplaced without discontinuing cooling and/or dehumidificationoperations. The valve may be actuated manually, or by using a controlsystem, such as the control system 64 embodiment depicted in FIG. 20.Additionally, the bypass valve 316 may be used to optimize the coolingand drying. For example, the bypass valve 316 may be used to reduce thenumber of cooling and drying stages in use by the HVAC system 300 whenit is desired to lower the cooling and drying capabilities of the HVACsystem 300 (e.g., in hot, dry weather). Likewise, the bypass valve 318may be actuated open (or partially open) in warmer, more humid weather,to include use of the cooling and dehumidification stages disposed insection 308.

FIG. 20 is a schematic diagram of an HVAC system 300 of FIG. 19including the control system 64. The control system 64 may becommunicatively coupled to various components of the HVAC system 300,including the pumps 60, 62, and 302, the evaporative cooling units 152,and the bypass valve 318. In certain embodiments, the control system 64may be configured to control the rate of removal of the noncondensablecomponents 30 of the water vapor 26A in the water vapor vacuum volume 28by turning the vacuum pumps 62 on or off, or by modulating the rate atwhich the multi-stage vacuum pump 302 removes the noncondensablecomponents 30. More specifically, in certain embodiments, the controlsystem 64 may receive signals from sensors in the water vapor vacuumvolume 28 that detect when too many noncondensable components 30 arepresent in the water vapor 26A contained in the water vapor vacuumvolume 28.

The control system 64 may modulate the lower partial pressure of thewater vapor 26A in the water vapor vacuum volume 28 of each stage 304and 306 to modify the water vapor removal capacity and efficiency ratioof the dehumidification units 12. For example, the control system 64 mayreceive signals from pressure sensors in the water vapor vacuum volumes28, the water vapor channels 18, as well as signals generated by sensorsrelating to characteristics (e.g., temperature, pressure, flow rate,relative humidity, and so forth) of the air 14 in the dehumidificationunits 12, the evaporative cooling units 152, or both units 12 and 152,among other components.

The control system 64 may use this information to determine how tomodulate the lower partial pressure of the water vapor 26A in the watervapor vacuum volume 28 to increase or decrease the rate of removal ofwater vapor 26 from the air channels 16 to the water vapor channels 18through the interfaces 20 of the dehumidification units 12 as H₂O (i.e.,as water molecules, gaseous water vapor, liquid water, adsorbed/desorbedwater molecules, absorbed/desorbed water molecules, and so forth,through the interfaces 20). For example, if more water vapor removal isdesired, the lower partial pressure of the water vapor 26A in the watervapor vacuum volume 28 may be reduced and, conversely, if less watervapor removal is desired, the lower partial pressure of the water vapor26A in the water vapor vacuum volume 28 may be increased. Furthermore,as described above, the amount of dehumidification (i.e., water vaporremoval) may be cycled to improve the efficiency of the dehumidificationunits 12. More specifically, under certain operating conditions, thedehumidification units 12 may function more efficiently at higher ratesof water vapor removal. As such, in certain embodiments, thedehumidification units 12 may be cycled to remove a maximum amount ofwater vapor from the air 14 for a period of time (e.g., approximately 1sec, 10 sec, 100 sec, 10 min), then to remove relatively no water vaporfrom the air 14 for a period of time (e.g., approximately 1 sec, 10 sec,100 sec, 10 min), then to remove a maximum amount of water vapor fromthe air 14 for a period of time (e.g., approximately 1 sec, 10 sec, 100sec, 10 min), and so forth. In other words, the dehumidification units12 may be operated at full water vapor removal capacity for periods oftime alternating with other periods of time where no water vapor isremoved. In one embodiment, modulation of the partial pressure of thewater vapor 26A may be accomplished by opening and closing (partially orfully) one or more valves (not shown) disposed on each inlet 310 and312. Indeed, each inlet 310 and 312 may include one or more valvessuitable for controlling flow through the inlet.

Furthermore, the control system 64 may also be configured to controloperation of the evaporative cooling units 152. For example, the controlsystem 64 may selectively modulate how much (direct or indirect)evaporative cooling occurs in the evaporating cooling units 152. As anexample, valves may be actuated to control the flow rate of therelatively cool and moist media 156 through the evaporative coolingunits 152, thereby directly affecting the amount of (direct or indirect)evaporative cooling in the evaporative cooling units 152. In addition,operation of the dehumidification units 12 and the evaporative coolingunits 152 may be controlled simultaneously. Furthermore, the controlsystem 64 may be configured to control start-up and shutdown sequencingof the dehumidification units 12 and the evaporative cooling units 152.Indeed, by controlling the several cooling and dehumidification stages304 and 306, and the multi-stage pump 302 of the HVAC system 300, thecontrol system 64 may enable a more energy efficient, reliable HVACsystem 300 suitable for producing cooler, lower humidity air 14F.

It is to be noted that the stage 304 and/or the stage 306 may bereplaced by other cooling and/or dehumidification systems. For example,rather than using an evaporative cooling unit, a mechanical cooling unitmay be used. Indeed, the HVAC system 300 may include embodiments where amechanical cooling unit, such as the mechanical cooling unit 236described above with respect to FIGS. 16 and 17, may replace each of theevaporative cooling units 152 depicted in FIG. 20. In this embodiment,sensible compression cooling may be provided by the mechanical coolingunit 236. Additionally or alternatively, the multi-stage vacuum pump 302may be used with cooling and dehumidification stages 304 and 306disposed in parallel, as described in more detail below with respect toFIG. 21. Further, the multi-stage pump 302 may be replaced by multiplesingle stage pumps (e.g., pumps 52). Additionally, multiple pumps 52described in all the embodiments herein, may be replaced with a singlemulti-stage pump 302, each stage of the multi-stage pump 302corresponding to one of the pumps 52.

FIG. 21 is a schematic view illustrating an embodiment of an HVAC system320 using the multi-stage vacuum pump 302 with the cooling anddehumidification stages 304 and 306 disposed in parallel. Also depictedis a section 322 of the HVAC system 320 that may include one or morecooling and dehumidification stages also disposed in parallel. Indeed,3, 4, 5, 6, 7, 8, 9, 10 or more cooling and dehumidification stages maybe disposed in parallel and connected to the multi-stage vacuum pump 302having multiple inlets 310 and 312. Additionally, sections 324 and 326may include further cooling and dehumidification stages disposed inseries. Thus the HVAC system 320 may include cooling anddehumidification stages disposed in parallel and in series. In addition,the control system 64 may also be used to control the HVAC system 320.

As illustrated may of the components, including but not limited to thecomponents 152, 12, 62, 54, 58, 302, and 60 may be considered identicalto the components of the HVAC system 300 of FIG. 20. For example, asdescribed previously with respect to the HVAC system 300 of FIG. 20,each stage 304 and 306 includes the evaporative cooling unit 152 ofFIGS. 19 and 20, which may either be a direct evaporative cooling unitor an indirect evaporative cooling unit that function as describedabove. The evaporative cooling unit 152 may be disposed upstream of thedehumidification unit 12. Relatively humid inlet air 14A may enter inparallel into the evaporative cooling units 152. The relatively humidinlet air 14A is then first cooled in parallel in each of theevaporative cooling units 152 and expelled as cooler air 14B into theducts 154. The dehumidification units 12 then reduce the humidity of theair 14B, and expel cooler dry air 14C into the conditioned space.Sections 324 and 326 may include multiple cooling and dehumidificationstages suitable for further cooling and drying the air 14C.

In the depicted embodiment, each of the dehumidification units 12 isdepicted as fluidly coupled to the inlets 310 and 312 of multi-stagepump 302. Indeed, the multi-stage pump 302 may include a stage and aninlet corresponding to each cooling and dehumidification stage.Therefore, if 2 stages are used, 2 inlets are included, if 4 stages areused, 4 inlets are included, if 10 stages are used, 10 inlets areincluded, and so on. In the depicted embodiment, the multi-stage pump402 may be used, for example by the control system 64, to modulate thelower partial pressure of the water vapor 26A in the water vapor vacuumvolume 28 of each stage 304 and 306 to modify the water vapor removalcapacity and efficiency ratio of the dehumidification units 12. In oneexample, the water vapor removal capacity and the efficiency ratio ofeach of the dehumidification units 12 may be approximately similar. Inother examples, the water vapor removal capacity and efficiency ratiomay be varied between dehumidification units 12, for example, to providecooler or warmer air, and for drier or more humid air. For example, ifmore water vapor removal is desired, the lower partial pressure of thewater vapor 26A in the water vapor vacuum volume 28 may be reduced and,conversely, if less water vapor removal is desired, the lower partialpressure of the water vapor 26A in the water vapor vacuum volume 28 maybe increased. Furthermore, as described above, the amount ofdehumidification (i.e., water vapor removal) may be cycled to improvethe efficiency of the dehumidification units 12.

The condensation unit 54 receives water vapor 26B having a partialpressure just high enough to facilitate condensation from an outlet ofthe multi-stage pump 302. In certain embodiments, the HVAC system 320 ofFIG. 21 may also include the reservoir 58 for temporary storage ofsaturated vapor and liquid water. However, as described previously, inother embodiments, no reservoir may be used. In either case, the liquidwater from the condensation unit 54 may be directed into the liquid pump60, within which the pressure of the liquid water from the condensationunit 54 is increased to approximately atmospheric pressure (i.e.,approximately 14.7 psia) so that the liquid water may be rejected atambient conditions. Additionally, or alternatively, a low pressure sidemay include the vacuum pump 62 useful in purging noncondensablecomponents 30.

Additionally HVAC system's 320 flexibility may be provided by turning onor off certain number of cooling and dehumidification stages. Forexample, the control system 64 may turn on or off the stage 304 or thestage 306 to provide for differing cooling and/or dehumidificationcapacities, or for system maintenance. For example, if maintenance onthe stage 304 is desired, it may be turned off while the stage 306 isallowed to continue operations. Likewise, stage 306 may be turned offwhile stage 304 is operating. Additionally, each stage 304 and 306 maybe disposed in a different floor or room of a building, thus enablingfor multi-zone cooling and dehumidification. Further, the multi-stagevacuum pump may be used to modulate cooling and dehumidification of anystage disposed in parallel, in series, or a combination thereof, thusproviding for differing cooling and dehumidification for various zones.

FIG. 22 is a schematic view illustrating an embodiment of the HVACsystem 330 including multiple dehumidification units 74 and 78 disposedin series with the mechanical cooling unit 236 disposed downstream ofthe dehumidification units 74 and 78. The dehumidification units 74 and78 are equivalent to the dehumidification unit 12 described above. Alsodepicted is a section 332 which may include 2, 3, 4, 5, 6, 7, 8, 9, 10or more dehumidification units disposed in series. Because water vaporis removed from each successive dehumidification unit 74, 78, thepartial pressure of water vapor in the air 14 will be gradually reducedat each successive dehumidification unit 74, 78. For example, asdescribed previously, the partial pressure of water vapor in the inletair 14A may be in the range of approximately 0.2-1.0 psia; the partialpressure of water vapor in the air 14B from the first dehumidificationunit 74 may be in the range of approximately 0.17-0.75 psia(accomplishing approximately ⅓ of the drop); the partial pressure ofwater vapor in the air 14C from a second dehumidification unit (notshown) disposed in section 332 may be in the range of approximately0.14-0.54 psia (accomplishing approximately the next ⅓ of the drop); andthe partial pressure of water vapor in the outlet air 14D from the thirddehumidification unit 78 may be in the range of approximately 0.10-0.25psia, which is consistent with a 60° F. saturation temperature or lower.The very low values may be used to increase capacity for occasional use.

As such, in certain embodiments, the partial pressure of water vapor inthe water vapor vacuum volumes 90, 94 (e.g., that are similar infunctionality to the water vapor vacuum volume 28 described previously)associated with each respective vacuum pump 84, 88 may be modulated toensure an optimal flow of water vapor 26A from each respectivedehumidification unit 74, 78. For example, the partial pressure of thewater vapor 26A in the water vapor vacuum volume 28 described previouslymay be maintained in a range of approximately 0.15-0.25 psia. However,in the HVAC system 330 of FIG. 22, the partial pressure of the watervapor 26A in the first water vapor vacuum volume 90 may be maintained ina range of approximately 0.15-0.7 psia, the partial pressure of thewater vapor 26A in a second water vapor vacuum volume of a singledehumidification unit (not shown) disposed in section 332 may bemaintained in a range of approximately 0.12-0.49 psia, and the partialpressure of the water vapor 26A in the third water vapor vacuum volume94 may be maintained in a range of approximately 0.09-0.24 psia.Regardless, it may be expected that less water vapor 26 will be removedin each successive dehumidification unit 74, 78, and may generally beoptimized to minimize energy used to operate the system 330.

In certain embodiments, each of the vacuum pumps 84, 88 may compress thewater vapor 26 and direct it into a common manifold 96 having asubstantially constant partial pressure of water vapor (i.e., just highenough to facilitate condensation in the condensation unit 54) such thatthe water vapor 26 flows in a direction opposite to the flow of the air14. In other embodiments, the water vapor 26 extracted from eachsuccessive dehumidification unit 74, 78 may be compressed by itsrespective vacuum pump 84, 88 and then combined with the water vapor 26extracted from the next upstream dehumidification unit 74, 78. Forexample, in other embodiments, the water vapor 26 from thedehumidification unit 78 may be compressed by the third vacuum pump 88and then combined with the water vapor 26 from the dehumidification unit74 in the second water vapor vacuum volume 90. In this embodiment, theexhaust side of each successive vacuum pump 84, 88 increases the partialpressure of the water vapor 26 only to the operating pressure of thenext upstream vacuum pump 84, 88. In this embodiment, the water vapor 26compressed by the first vacuum pump 84 will be directed into thecondensation unit 54 at a partial pressure of water vapor just highenough to facilitate condensation, thus increasing efficiency.

It should be noted that the specific embodiment illustrated in FIG. 22having a plurality of dehumidification units 74, 78 arranged in seriesmay be configured in various ways not illustrated in FIG. 22. Forexample, although illustrated as using a respective vacuum pump 84, 88with each dehumidification unit 74, 78, in certain embodiments, thesingle multi-stage vacuum pump 302 described above with respect to FIGS.19, 20, and 21 may be used with multiple inlet ports 310 and 312connected to the first, and second water vapor vacuum volumes 90, 94,respectively. In addition, although illustrated as using a singlecondensation unit 54, reservoir 58, and liquid pump 60 to condense thewater vapor 26B into a liquid state, and store and/or transport theliquid water from the HVAC system 330, in other embodiments, each set ofdehumidification units 74, 78 and vacuum pumps 84, 88 may be operatedindependently and be associated with their own respective condensationunits 54, reservoirs 58, and liquid pumps 60.

Additionally, the low humidity air 14D may then be cooled by themechanical cooling unit 236. Alternative or additional to the mechanicalcooling unit 236, the evaporative cooling unit 152 described above maybe used. In addition, the control system 64 may also be used to controlthe operation of the HVAC system 330 in a similar manner as describedpreviously with respect to FIGS. 7 and 8. For example, as describedpreviously, the control system 64 may be configured to control the rateof removal of the noncondensable components 30 of the water vapor 26 inthe water vapor vacuum volumes 90, 94 by turning the vacuum pumps 84, 88(or separate vacuum pumps 62, as described previously with respect toFIGS. 7 and 8) on or off, or by modulating the rate at which the vacuumpumps 84, 88 (or separate vacuum pumps 62, as described previously withrespect to FIGS. 7 and 8) remove the noncondensable components 30. Morespecifically, in certain embodiments, the control system 64 may receivesignals from sensors in the water vapor vacuum volumes 90, 94 thatdetect when too many noncondensable components 30 are present in thewater vapor 26A contained in the water vapor vacuum volumes 90, 94.

In addition, the control system 64 may modulate the lower partialpressure of the water vapor 26A in the water vapor vacuum volumes 90, 94to modify the water vapor removal capacity and efficiency ratio of thedehumidification units 74, 78. For example, the control system 64 mayreceive signals from pressure sensors in the water vapor vacuum volumes90, 94, the water vapor channels 18, as well as signals generated bysensors relating to characteristics (e.g., temperature, pressure, flowrate, relative humidity, and so forth) of the air 14, among otherthings. The control system 64 may use this information to determine howto modulate the lower partial pressure of the water vapor 26A in thewater vapor vacuum volumes 90, 94 to increase or decrease the rate ofremoval of water vapor 26 from the air channels 16 to the water vaporchannels 18 through the interfaces 20 of the dehumidification units 74,78 as H₂O (i.e., as water molecules, gaseous water vapor, liquid water,adsorbed/desorbed water molecules, absorbed/desorbed water molecules,and so forth, through the interfaces 20).

For example, if more water vapor removal is desired, the lower partialpressure of the water vapor 26A in the water vapor vacuum volumes 90, 94may be reduced and, conversely, if less water vapor removal is desired,the lower partial pressure of the water vapor 26A in the water vaporvacuum volumes 90, 94 may be increased. Furthermore, as described above,the amount of dehumidification (i.e., water vapor removal) may be cycledto improve the efficiency of the dehumidification units 74, 78. Morespecifically, under certain operating conditions, the dehumidificationunits 74, 78 may function more efficiently at higher rates of watervapor removal. As such, in certain embodiments, the dehumidificationunits 74, 78 may be cycled to remove a maximum amount of water vaporfrom the air 14 for a period of time (e.g., approximately 1 sec, 10 sec,100 sec, 10 min), then to remove relatively no water vapor from the air14 for a period of time (e.g., approximately 1 sec, 10 sec, 100 sec, 10min), then to remove a maximum amount of water vapor from the air 14 fora period of time (e.g., approximately 1 sec, 10 sec, 100 sec, 10 min),and so forth. In other words, the dehumidification units 74, 78 may beoperated at full water vapor removal capacity for periods of timealternating with other periods of time where no water vapor is removed.Further, the control system 64 may be used to control the mechanicalcooling unit 236, for example, by actuating the compressor to increaseor decrease compression and cooling. In addition, the control system 64may be configured to control start-up and shutdown sequencing of thedehumidification units 74, 78, the mechanical cooling unit 236, and theHVAC system 330. While FIG. 22 includes a disposition of the mechanicalcooling unit 236 downstream of the dehumidification and cooling units74, 78, other arrangements are contemplated herein. For example, FIG. 23depicts an upstream arrangement of the mechanical cooling unit 236.

More specifically, FIG. 23 is schematic view of an embodiment of an HVACsystem 334 including the mechanical cooling 236 disposed in seriesupstream of the dehumidification units 74, 78, and the section 332.Because the figure includes similar elements to FIG. 22, like numbersare used to denote like elements. In the depicted embodiment, hot, humidair 14A enters the mechanical cooling unit 236. The mechanical coolingunit 236 may then cool (and slightly dry) the air 14, resulting in acooler (and slightly drier) air 14B. The air 14B may then be furtherdried by the cooling units 74, 78, and the section 332 as describedabove, to produce the air 14E having a drier state when compared to theair 14B. Additionally, the control system 64 may also be configured tocontrol start-up and shutdown sequencing of the dehumidification units74, 78, the mechanical cooling unit 236, and the HVAC system 334.Additional or alternative to the mechanical cooling unit 236, theevaporative cooling unit 152 may be provided, thus enhancing the coolingabilities of the HVAC system 334.

While FIG. 23 includes a serial arrangement of multiple dehumidificationunits 74, 78, present embodiments include other ways in which multipledehumidification units 74, 78 may be arranged in a single HVAC system.For example, FIG. 24 depicts a parallel arrangement of thedehumidification units 100 and 104. More specifically, FIG. 24 is aschematic view of an embodiment of an HVAC system 336 including thedehumidification units 100, 104 disposed in parallel, and the mechanicalcooling unit 236 disposed downstream from the dehumidification units100, 104. Each of the dehumidification units 100, 104 is substantiallythe same as the dehumidification unit 12. Although illustrated as havingtwo dehumidification units 100, 104 in parallel, any number ofdehumidification units may indeed be used in parallel in the HVAC system336. For example, in other embodiments, 2, 4, 5, 6, 7, 8, 9, 10, or evenmore dehumidification units may be used in parallel in the HVAC system336. For example, a section 338 may be used to dispose additionaldehumidification units in parallel.

The HVAC system 336 of FIG. 24 generally functions the same as the HVACsystem 10 of FIGS. 1, 6, and 7 and the HVAC system 98 of FIG. 9, butwith the addition of a single mechanical cooling unit 236. It is to beunderstood that, in other embodiments, each of the dehumidificationunits 100, 104 may include a corresponding mechanical cooling unit 236.As illustrated in FIG. 24, each dehumidification unit 100, 104 of theHVAC system 336 receives the inlet air 14A having a relatively highhumidity and expels the outlet air 14B having a relatively low humidity.As illustrated, many of the components of the HVAC system 336 of FIG. 24may be considered identical to the components of the HVAC system 10 ofFIGS. 1, 6, and 7, the HVAC system 98 of FIG. 9, and the HVAC system 334of FIG. 23. For example, the dehumidification units 100, 104 of the HVACsystem 336 of FIG. 24 may be considered identical to thedehumidification units 12 of FIGS. 1, 6, and 7. In addition, the HVACsystem 336 of FIG. 24 also includes the condensation unit 54 thatreceives water vapor 26B having a partial pressure just high enough tofacilitate condensation, as described previously. In certainembodiments, the HVAC system 336 of FIG. 24 may also include thereservoir 58 for temporary storage of saturated vapor and liquid water.However, as described previously, in other embodiments, no reservoir maybe used. In either case, the liquid water from the condensation unit 54may be directed into the liquid pump 60, within which the pressure ofthe liquid water from the condensation unit 54 is increased toapproximately atmospheric pressure (i.e., approximately 14.7 psia) sothat the liquid water may be rejected at ambient conditions.

As illustrated in FIG. 24, in certain embodiments, each dehumidificationunit 100, 104 may be associated with a respective vacuum pump 106, 110,each of which is similar in functionality to the vacuum pump 52 of FIGS.1, 6, and 7. However, as opposed to the HVAC system 334 of FIG. 23,because the dehumidification units 100, 104 and associated vacuum pumps106, 110 are arranged in parallel, the partial pressure of water vaporin the air 14 will be approximately the same in each dehumidificationunit 100, 104. As such, in general, the partial pressure of water vaporin the water vapor vacuum volumes 112, 116 associated with eachrespective vacuum pump 106, 110 will also be approximately the same. Forexample, as described previously with respect to the HVAC system 10 ofFIGS. 1, 6, and 7, the partial pressure of the water vapor 26A in thewater vapor vacuum volumes 112, 116 may be maintained in a range ofapproximately 0.10-0.25 psia.

As illustrated in FIG. 24, in certain embodiments, each of the vacuumpumps 106, 110 may compress the water vapor 26 and direct it into acommon manifold 118 having a substantially constant partial pressure ofwater vapor (i.e., just high enough to facilitate condensation in thecondensation unit 54). In other embodiments, the water vapor 26extracted from each successive dehumidification unit 100, 104 (i.e.,from top to bottom) may be compressed by its respective vacuum pump 106,110 and then combined with the water vapor 26 extracted from the nextdownstream (i.e., with respect to the common manifold) dehumidificationunit 100, 104. For example, in other embodiments, the water vapor 26from the first dehumidification unit 100 may be compressed by the firstvacuum pump 106 and then combined with the water vapor 26 from thesecond dehumidification unit 104 in the second water vapor vacuum volume116. In this embodiment, the exhaust side of each successive vacuum pump106, 110 increases the partial pressure of the water vapor 26 only tothe operating pressure of the next downstream vacuum pump 106, 110. Forexample, the first vacuum pump 106 may only increase the pressure of thewater vapor 26 to approximately 0.2 psia if the partial pressure ofwater vapor in the second water vapor vacuum volume 116 is approximately0.2 psia. In this embodiment, the water vapor 26 compressed by thevacuum pump 110 will be directed into the condensation unit 54 at apartial pressure of water vapor just high enough to facilitatecondensation.

It should be noted that the specific embodiment illustrated in FIG. 24having a plurality of dehumidification units 100, 104 arranged inparallel may be configured in various ways not illustrated in FIG. 24.For example, although illustrated as using a respective vacuum pump 106,110 with each dehumidification unit 100, 104, in certain embodiments,the single multi-stage vacuum pump 302 may be used with multiple inletports 310, 312 connected to the first and second water vapor vacuumvolumes 112, 116. In addition, although illustrated as using a singlecondensation unit 54, reservoir 58, and liquid pump 60 to condense thewater vapor 26B into a liquid state, and store and/or transport theliquid water from the HVAC system 336, in other embodiments, each set ofdehumidification units 100, 104 and vacuum pumps 106, 110 may beoperated independently and be associated with their own respectivecondensation units 54, reservoirs 58, and liquid pumps 60.

In addition, the control system 64 may also be used in the HVAC system336 of FIG. 24 to control the operation of the HVAC system 336 in asimilar manner as described previously with respect to FIG. 9. Forexample, as described previously, the control system 64 may beconfigured to control the rate of removal of the noncondensablecomponents 30 of the water vapor 26A in the water vapor vacuum volumes112, 116 by turning the vacuum pumps 106, 110 (or separate vacuum pumps62, as described previously with respect to FIGS. 7 and 9) on or off, orby modulating the rate at which the vacuum pumps 106, 110 (or separatevacuum pumps 62, as described previously with respect to FIGS. 7 and 9)remove the noncondensable components 30. More specifically, in certainembodiments, the control system 64 may receive signals from sensors inthe water vapor vacuum volumes 112, 116 that detect when too manynoncondensable components 30 are present in the water vapor 26Acontained in the water vapor vacuum volumes 112, 116.

In addition, the control system 64 may modulate the lower partialpressure of the water vapor 26A in the water vapor vacuum volumes 112,116 to modify the water vapor removal capacity and efficiency ratio ofthe dehumidification units 100, 104. For example, the control system 64may receive signals from pressure sensors in the water vapor vacuumvolumes 112, 116, the water vapor channels 18, as well as signalsgenerated by sensors relating to characteristics (e.g., temperature,pressure, flow rate, relative humidity, and so forth) of the air 14,among other things. The control system 64 may use this information todetermine how to modulate the lower partial pressure of the water vapor26A in the water vapor vacuum volumes 112, 116 to increase or decreasethe rate of removal of water vapor 26 from the air channels 16 to thewater vapor channels 18 through the interfaces 20 of thedehumidification units 100, 102, 104 as H₂O (i.e., as water molecules,gaseous water vapor, liquid water, adsorbed/desorbed water molecules,absorbed/desorbed water molecules, and so forth, through the interfaces20).

For example, if more water vapor removal is desired, the lower partialpressure of the water vapor 26A in the water vapor vacuum volumes 112,116 may be reduced and, conversely, if less water vapor removal isdesired, the lower partial pressure of the water vapor 26A in the watervapor vacuum volumes 112, 116 may be increased. Furthermore, asdescribed above, the amount of dehumidification (i.e., water vaporremoval) may be cycled to improve the efficiency of the dehumidificationunits 100, 104. More specifically, under certain operating conditions,the dehumidification units 100, 104 may function more efficiently athigher rates of water vapor removal. As such, in certain embodiments,the dehumidification units 100, 104 may be cycled to remove a maximumamount of water vapor from the air 14 for a period of time (e.g.,approximately 1 sec, 10 sec, 100 sec, 10 min), then to remove relativelyno water vapor from the air 14 for a period of time (e.g., approximately1 sec, 10 sec, 100 sec, 10 min), then to remove a maximum amount ofwater vapor from the air 14 for a v (e.g., approximately 1 sec, 10 sec,100 sec, 10 min), and so forth. In other words, the dehumidificationunits 100, 104 may be operated at full water vapor removal capacity forperiods of time alternating with other periods of time where no watervapor is removed. In addition, the control system 64 may be configuredto control start-up and shutdown sequencing of the dehumidificationunits 100, 104, the mechanical cooling unit 236, and the HVAC system336.

While FIG. 24 includes a disposition of the mechanical cooling unit 236downstream of the dehumidification and cooling units 100, 104, otherarrangements are contemplated herein. For example, FIG. 25 depicts anupstream arrangement of the mechanical cooling unit 236. Morespecifically, FIG. 25 is schematic view of an embodiment of an HVACsystem 340 including the mechanical cooling 236 disposed in seriesupstream of the dehumidification units 100, 104, and the section 338.Because the figure includes similar elements to FIG. 24, like numbersare used to denote like elements. In the depicted embodiment, hot, humidair 14A enters the mechanical cooling unit 236. The mechanical coolingunit 236 may then cool (and slightly dry) the air 14, resulting in acooler (and slightly drier) air 14B. The air 14B may then be furtherdried by the cooling units 100, 104 and the section 338 as describedabove, to produce the air 14C having a drier state when compared to theair 14B. Additionally, the control system 64 may also be configured tocontrol start-up and shutdown sequencing of the dehumidification units100, 104, the mechanical cooling unit 236, and the HVAC system 340.Additional or alternative to the mechanical cooling unit 236, theevaporative cooling unit 152 may be provided, thus enhancing the coolingabilities of the HVAC system 340.

In addition to the serial arrangement of dehumidification units 74, 78illustrated in FIGS. 22 and 23, and the parallel arrangement ofdehumidification units 100, 104 illustrated in FIGS. 24 and 25, multipledehumidification units may be used in other ways. Indeed, much morecomplex and expansive arrangements may also be used. For example, FIG.26 is a schematic diagram of an HVAC system 342 having a first set 122of dehumidification units (i.e., a first dehumidification unit 124 and asecond dehumidification unit 126) arranged in series, and a second set128 of dehumidification units (i.e., a third dehumidification unit 130and a fourth dehumidification unit 132) also arranged in series, withthe first and second sets 122, 128 of dehumidification units arranged inparallel in accordance with an embodiment of the present disclosure.Additionally, a section 344 may be used to dispose furtherdehumidification units in series and in parallel. In other words, thefirst set 122 of serial first and second dehumidification units 124, 126are arranged in parallel with the second set 128 of serial third andfourth dehumidification units 130, 132. The dehumidification units 124,126, 130, and 132 are functionally equivalent to the dehumidificationunit 12 described above.

Although illustrated as having two sets 122, 128 of serialdehumidification units 12 arranged in parallel, any number of parallelpluralities of dehumidification units 12 may indeed be used in the HVACsystem 342. For example, in other embodiments, 3, 4, 5, 6, 7, 8, 9, 10,or even more parallel sets of dehumidification units may be used in theHVAC system 342. Similarly, although illustrated as having twodehumidification units arranged in series within each set 122, 128 ofdehumidification units, any number of dehumidification units may indeedbe used in series within each set 122, 128 of dehumidification units 12in the HVAC system 342. For example, in other embodiments, 1, 3, 4, 5,6, 7, 8, 9, 10, or even more dehumidification units may be used inseries within each set 122, 128 of dehumidification units 12 in the HVACsystem 342, such as dehumidification units disposed in sections 346 and348.

Substantially all of the operating characteristics of the HVAC system342 of FIG. 26 are similar to those described previously with respect tothe HVAC systems described in FIGS. 22-25. For example, as illustrated,each of the dehumidification units 124, 126, 130, 132 may be associatedwith its own respective vacuum pump 134, 136, 138, 140 (e.g., similar tothe vacuum pump 52 of FIGS. 1, 6, and 7). However, in other embodiments,one multi-stage vacuum pump 302 may be used for each set 122, 128 ofdehumidification units with multiple inlet ports connected to therespective water vapor vacuum volumes 142, 144, 146, 148. Indeed, inother embodiments, all of the dehumidification units 124, 126, 130, 132may be associated with the single multi-stage vacuum pump 302 withmultiple inlet ports connected to all of the water vapor vacuum volumes142, 144, 146, 148.

In addition, although illustrated as using a single condensation unit54, reservoir 58, and liquid pump 60 to condense the water vapor 26Binto a liquid state, and store and/or transport the liquid water fromthe HVAC system 342, in other embodiments, each set of dehumidificationunits 124, 126, 130, 132 and vacuum pumps 134, 136, 138, 140 may beoperated independently and be associated with their own respectivecondensation units 54, reservoirs 58, and liquid pumps 60. In addition,the control system 64 described previously may also be used in the HVACsystem 342 of FIG. 26 to control operation of the HVAC system 342 in asimilar manner as described previously.

The embodiments described previously with respect to FIGS. 19 through 26are slightly more complex than the embodiments described previously withrespect to FIGS. 1 through 7 inasmuch as multiple dehumidification unitsare used in series, parallel, or some combination thereof. As such, thecontrol of pressures and temperatures of the HVAC systems of FIGS. 19through 26 are slightly more complicated than the control of a singledehumidification unit 12. For example, the partial pressures in thewater vapor vacuum volumes may need to be closely monitored andmodulated by the control system 64 to take into account variations intemperature and partial pressure of water vapor in the air 14 within therespective dehumidification units 12, operating pressures of adjacentwater vapor vacuum volumes and vacuum pumps (which may be cross-pipedtogether as described previously to facilitate control of pressures,flows, and so forth), among other things. In certain embodiments,variable or fixed orifices may be used to control pressures and changesin pressures in and between the dehumidification units 12. In addition,as described previously, each of the respective vacuum pumps may becontrolled to adjust the partial pressures of water vapor in the watervapor vacuum volumes to account for variations between dehumidificationunits 12.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

1. A dehumidification system for removing water vapor from an airstream,comprising: at least one cooling unit configured to cool air; aplurality of dehumidification units fluidly coupled to the cooling unit,each dehumidification unit comprising a first and second channelseparated by a membrane, wherein the membrane is configured tofacilitate removal of water vapor from an airstream flowing through thefirst channel by facilitating passage of H₂O from the first channel tothe second channel through permeable volumes of the membrane whilesubstantially blocking all other components of the airstream frompassing through the membrane; at least one pressure increasing deviceconfigured to create a lower partial pressure of water vapor within thesecond channels than in the first channels, such that the H₂O movesthrough the membranes to the second channels, wherein the at least onepressure increasing device is also configured to increase the pressureof water vapor at an outlet of the at least one pressure increasingdevice to a partial pressure of water vapor in a range suitable forsubsequent condensing into liquid water; at least one condensationdevice configured to receive the water vapor from the at least onepressure increasing device and condense the water vapor into liquidwater; and at least one water transport device configured to transportthe liquid water from the at least one condensation device.
 2. Thesystem of claim 1, wherein the plurality of dehumidification units arearranged in series with each other such that the airstream flows throughthe first channel of each dehumidification unit in series.
 3. The systemof claim 1, wherein the plurality of dehumidification units are arrangedin parallel with each other such that the airstream flows through thefirst channel of only one dehumidification unit in parallel.
 4. Thesystem of claim 1, wherein a first set of the plurality ofdehumidification units is arranged in series with each other, a secondset of the plurality of dehumidification units is arranged in serieswith each other, and the first and second set of the plurality ofdehumidification units are arranged in parallel with each other.
 5. Thesystem of claim 1, wherein the at least one cooling unit comprises amechanical cooling unit, an evaporative cooling unit, or a combinationthereof.
 6. The system of claim 1, wherein the at least one cooling unitis disposed upstream of the plurality of dehumidification units,downstream of the plurality of dehumidification units, or a combinationthereof.
 7. The system of claim 1, wherein each of the plurality ofdehumidification units delivers water vapor from the second channel tothe same pressure increasing device.
 8. The system of claim 1, whereineach of the plurality of dehumidification units delivers water vaporfrom the second channel to a respective pressure increasing deviceassociated therewith.
 9. The system of claim 1, wherein a controller isconfigured to increase efficiency of the operation of thedehumidification system by substantially reducing an energy use.
 10. Thesystem of claim 9, wherein the at least one pressure increasing devicecomprises a vacuum pump, and wherein the controller is configured tosubstantially reduce the energy use by substantially reducing a pumpenergy used to drive the vacuum pump.
 11. A system, comprising: adehumidification system for removing H₂O vapor from an airstream,comprising: at least one cooling unit configured to cool air; aplurality of dehumidification units fluidly coupled to the at least onecooling unit, each dehumidification unit comprising an air channelconfigured to receive an inlet airstream and discharge an outletairstream, and an H₂O permeable barrier adjacent to the air channel,wherein the H₂O permeable barrier is configured to selectively enableH₂O from H₂O vapor in the inlet airstream to pass through the H₂Opermeable barrier to a suction side of the H₂O permeable barrier andsubstantially block other components in the inlet airstream from passingthrough the H₂O permeable barrier to the suction side of the H₂Opermeable barrier; and at least one pressure increasing deviceconfigured to create a lower partial pressure of H₂O vapor on thesuction sides of the H₂O permeable barriers than the partial pressure ofthe H₂O vapor in the inlet airstreams to drive passage of the H₂O fromthe H₂O vapor in the inlet airstream through the H₂O permeable barrier,and to increase the pressure at an outlet of the at least one pressureincreasing device to a partial pressure of H₂O vapor suitable forcondensing H₂O vapor into liquid H₂O.
 12. The system of claim 11,wherein the dehumidification system comprises at least one condensationdevice configured to receive the H₂O vapor from the outlet of the atleast one pressure increasing device, and to condense the H₂O vapor intoliquid H₂O.
 13. The system of claim 12, wherein the dehumidificationsystem comprises at least one device configured to adjust a pressure ofthe liquid H₂O from the at least one condensation device to an ambientpressure.
 14. The system of claim 11, wherein the dehumidificationsystem comprises at least one membrane water vapor rejection deviceconfigured to receive the H₂O vapor from the outlet of the at least onepressure increasing device, and to reject the H₂O vapor into an ambientair.
 15. The system of claim 11, wherein the plurality ofdehumidification units are arranged in series with each other such thatthe airstream flows through the air channel of each dehumidificationunit in series.
 16. The system of claim 11, wherein the plurality ofdehumidification units are arranged in parallel with each other suchthat the airstream flows through the air channel of only onedehumidification unit in parallel.
 17. The system of claim 11, wherein afirst set of the plurality of dehumidification units is arranged inseries with each other, a second set of the plurality ofdehumidification units is arranged in series with each other, and thefirst and second set of the plurality of dehumidification units arearranged in parallel with each other.
 18. The system of claim 11,wherein the H₂O permeable barriers comprise zeolite.
 19. A method,comprising: receiving a plurality of airstreams including H₂O vapor intoair channels of a plurality of dehumidification units, wherein theairstreams have a first partial pressure of H₂O vapor; suctioning H₂Ointo H₂O vapor channels of the plurality of dehumidification unitsthrough H₂O permeable materials of the plurality of dehumidificationunits using pressure differentials across the H₂O permeable materials,wherein the H₂O vapor channels have a second partial pressure of H₂Ovapor lower than the first partial pressure of H₂O vapor of theairstreams; receiving H₂O vapor from the H₂O vapor channels into apressure increasing device and increasing the pressure of the H₂O vaporfrom the pressure increasing device to a third partial pressure of H₂Ovapor that is higher than the second partial pressure of H₂O vapor;receiving the H₂O vapor from the pressure increasing device into acondensation device and condensing the H₂O vapor into liquid H₂O;transporting the liquid H₂O from the condensation device to ambientconditions; and cooling the airstreams by using at least one coolingunit.
 20. The method of claim 19, comprising receiving the plurality ofairstreams including H₂O vapor into air channels of the plurality ofdehumidification units arranged in series with each other such that theairstreams flow through the air channels of each dehumidification unitin series.
 21. The method of claim 19, comprising receiving theplurality of airstreams including H₂O vapor into air channels of theplurality of dehumidification units arranged in parallel with each othersuch that each of the airstreams flow through the air channel of onlyone dehumidification unit in parallel.
 22. The method of claim 19,comprising receiving the plurality of airstreams including H₂O vaporinto air channels of a first set of the plurality of dehumidificationunits arranged in series with each other, and a second set of theplurality of dehumidification units arranged in series with each other,wherein the first and second set of the plurality of dehumidificationunits are arranged in parallel with each other.
 23. The method of claim19, wherein cooling the airstreams occurs downstream of the receiving aplurality of airstreams, upstream of the receiving a plurality ofairstreams, or a combination thereof.